Bottomley arrived in Brighton in 1875 where he found work work at a jeweller's shop. He lived in a small garret bedroom over a chandler's shop at 3, Little East Street. During this period he was also a member of the local debating society. Bottomley eventually returned to London and in 1877 he found employment as an office boy in an ironworks in Euston Road and lodged with a widow in Battersea. He enrolled at Pitman's College and in 1879 joined a firm of legal shorthand writers, in Holywell Street.

Bottomley also worked as a proof-reader to George Jacob Holyoake and Charles Bradlaugh, another leading figure in the secular movement. His biographer, A. J. A. Morris has argued that: "Bottomley bore a striking resemblance to Bradlaugh - not in stature, for he was short and stout, but in features. He countenanced, even encouraged, the rumour that he was the natural child of the great Victorian freethinker." Henry J. Houston, who researched his life, claimed: "It was always a foolish rumour, and never had any more basis than a rather striking facial resemblance between the two men. If Bradlaugh had been Bottomley's father he was the type of man who would have looked after his son, and not left him to struggle with the world as he did in the early days." It is possible that Bottomley was the source of the rumour as he did not like the idea of his father dying in Bethleham Hospital.

In May 1880, Bottomley married a dressmaker's counter assistant, Eliza Norton (1860–1930), daughter of Samuel Norton, a debt collector of Battersea. According to Houston: "It is agreed by all who remember her in those days, a most attractive and pretty young lady. Her family was humble but eminently respectable." They had one child, a daughter. Bottomley now decided to become a journalist. He had a strong interest in politics and founded several journals that reported the debates of local parliaments. He quickly acquired a small group of magazines and journals that in 1885 constituted the Catherine Street Publishing Association. In 1888 he helped establish The Financial Times.

In 1889 he floated the Hansard Publishing Union. Within two years he was obliged to file for bankruptcy and was charged with conspiracy to defraud. It was generally assumed that he would be found guilty but, conducting his own defence brilliantly, he was acquitted. Bottomley now founded the Joint Stock Trust and Institute as the vehicle for floating the Western Australian gold mining companies he now promoted.

In 1897 The Financial Times reported that he was "a man of millions". Bottomley purchased a large house, The Dicker, near Eastbourne. He also had a second home in Monte Carlo, where his wife lived. A. J. A. Morris has pointed out: "He enjoyed many mistresses, preferring lively, petite, blonde, working-class girls. He always treated them with courtesy and generosity. The current favourites - he liked to have two if not three in tow at a time - were set up in rented flats and showered with flowers and gifts." Frank Harris, one of his friends, commented that he had an "intense greed for all the sensual pleasures".

One of the tasks of Henry J. Houston was to arrange his meetings with his many mistresses: In one respect at least, Horatio Bottomley resembled many of the most notable - and some of the most notorious - men in history. After every big physical and mental effort, whether in finance, the law, public oratory, journalism, or politics, he turned with unfailing regularity to the fair sex for solace, oblivion, and refreshment. Few men took more genuine delight in the society of women, and it is impossible to understand the character of the man without a knowledge of his attitude towards them.... For a public man he was amazingly reckless in his feminine friendships. Utterly devoid of conventional views on the relationship of the sexes, he was occasionally hard to convince that a public man was under an inescapable obligation to be circumspect in public. Repeatedly I have had to point out to him - not always with any effect - the unwisdom of travelling while on public business with a lady to whom he was not married, however innocent the association might be."

Bottomley also had a luxury apartment in Pall Mall and owned several racehorses. He twice won the Cesarewitch and several other races, but never achieved the successes in the Derby or the Grand National, even though he spent a great deal of money trying to achieve this ambition. He also lost a great deal of money on failed betting coups.

In 1902 Bottomley bought the evening newspaper, The Sun. He was unable to increase its circulation and he sold the newspaper in 1904. Two years later, with the support of the Odham's Press, he launched the John Bull Magazine in May 1906. The journal's masthead asserted that it was written "without fear or favour, rancour or rant" to uphold the interests of the common man.

Bottomley desired a career in politics and after joining the Liberal Party, he was elected to represent Hackney South in the 1906 General Election. By this time there were rumours about his business activities. In one debate in the House of Commons he described himself as the chancellor's "more or less honourable friend". He did not help his case by saying that all political parties "are organised hypocrisies" and political leaders "for the most part do nothing or seek only to serve their own ends".

Bottomley appointed Henry J. Houston as his personal assistant just before the 1910 General Election. He later recalled: "I had for a long time been a close student of politics, working ardently for my local political association, and I followed with interest the political work of Horatio Bottomley." Bottomley was no longer a supporter of the Liberal government and rejected the Liberal whip, and claiming he preferred "to occupy a position of dignified detachment". He formed the John Bull League and called on an alliance with right-wing MPs in order "to continue to criticise the Liberal party unhampered by Cobdenite shibboleths". He argued for the government of Herbert Henry Asquith to be replaced by one of business leaders.

In February 1912, facing demands from the Prudential Assurance Company, he admitted that his liabilities exceeded his assets by £200,000. As a bankrupt he could no longer remain an MP and on 24th May, he left the House of Commons.

On the outbreak of the First World War, Bottomley told his personal assistant, Henry J. Houston: "Houston, this war is my opportunity. Whatever I have been in the past, and whatever my faults, I am going to draw a line at August 4th, 1914, and start afresh. I shall play the game, cut all my old associates, and wipe out everything pre-1914" Houston later recalled: "At the time I thought he meant it, but but now I know that the flesh, habituated to luxury and self-indulgence, was too weak to give effect to the resolution. For a while he did try to shake off his old associates, but the claws of the past had him grappled in steel, and the effort did not last more than a few weeks."

In September 1914, the first recruiting meetings were held in London. The first meetings were addressed by government ministers. Bottomley told Houston: "These professional politicians don't understand the business. I am going to constitute myself the Unofficial Recruiting Agent to the British Empire. We must have a big meeting." His first meeting at the Albert Hall was so popular that according to Houston, Bottomley "was unable for two hours to get into his own meeting."

Bottomley wrote to Herbert Henry Asquith about the possibility of becoming Director of Recruiting. Asquith replied: "Thank you for your offer but I shall not avail myself of it at the moment. You are doing better work where you are." Asquith, aware of his popularity, encouraged him to do this work in an unofficial capacity. It has been claimed at the time that he was paid between £50 and £100 to address meetings where he encouraged young men to join the armed forces. Henry J. Houston claimed that he spoke at the Empire Theatre, Leicester Square, and delivered a ten minutes' speech each night for a week at a fee of £600. Later, Bottomley "secured a week's engagement, two houses nightly, at the Glasgow Pavilion, where he received a fee of £1,000."

In 1914 David Lloyd George, the Chancellor of the Exchequer, was given the task of setting up a British War Propaganda Bureau (WPB). Lloyd George, appointed the successful writer and fellow Liberal MP, Charles Masterman as head of the organization. The WPB arranged for journalists like Bottomley to visit the Western Front.

It has been calculated that Bottomley addressed twenty recruiting meetings and 340 "patriotic war lectures". Although he had been highly critical of the government, at the meetings he always stated: "When the country is at war, it is the duty of every patriot to say: My country right or wrong; My government good or bad." He also falsely claimed that he was "not going to take money for sending men out to their death, or profit from his country in its hour of need." Bottomley claimed that he used the meetings to publicise John Bull Magazine and according to Houston, he drew over £22,000 from the journal for his efforts.

At one meeting a man in the audience shouted out: "Isn't it time you went and did your bit, Mr. Bottomley?" Bottomley replied: "Would to God it were my privilege to shoulder a rifle and take my place beside the brave boys in the trenches. But you have only to look at me to see that I am suffering from two complaints. My medical man calls them anno domini and embonpoint. The first means that I was born too soon and the second that my chest measurement has got into the wrong place."

To persuade young men to join the armed forces he gave the impression that the war would be over in a few weeks. In a speech at the Bournemouth Winter Gardens in September, 1915, he argued: "Ladies and gentlemen, I want you to pull yourselves together and keep your peckers up. I want to assure you that within six weeks of to-day we shall have the Huns on the run. We shall drive them out of France, out of Flanders, out of Belgium, across the Rhine, and back into their own territory. There we shall give them a taste of their own medicine. Bear in mind, I speak of that which I know. Tomorrow it will be officially denied, but take it from me that if Bottomley says so, it is so!"

Houston argued in his book, The Real Horatio Bottomley (1923): "He began to accept what were practically music hall engagements disguised as recruiting meetings, and I was very definitely of the opinion that he was drifting in the wrong direction. Nevertheless for some time it went on... Bottomley insisted that a substantial contribution (from the income generated from the meetings) went to his War Charity Fund... Three years later I discovered that the fund did not receive a penny of the money."

In one speech Bottomley argued: "Every hero of the war who has fallen in the field of battle has performed an Act of Greatest Love, so penetrating and intense in its purifying character that I do not hesitate to express my opinion that any and every past sin is automatically wiped out from the record of his life." George Bernard Shaw went to one of Bottomley's meetings and afterwards commented: "It's exactly what I expected: the man gets his popularity by telling people with sufficient bombast just what they think themselves and therefore want to hear."

Bottomley argued in the John Bull Magazine that Ramsay MacDonald and James Keir Hardie, were the leaders of a "pro-German Campaign". On 19th June 1915 the magazine claimed that MacDonald was a traitor and that: "We demand his trial by Court Martial, his condemnation as an aider and abetter of the King's enemies, and that he be taken to the Tower and shot at dawn."

On 4th September, 1915, the magazine published an article which made an attack on his background. "We have remained silent with regard to certain facts which have been in our possession for a long time. First of all, we knew that this man was living under an adopted name - and that he was registered as James MacDonald Ramsay - and that, therefore, he had obtained admission to the House of Commons in false colours, and was probably liable to heavy penalties to have his election declared void. But to have disclosed this state of things would have imposed upon us a very painful and unsavoury duty. We should have been compelled to produce the man's birth certificate. And that would have revealed what today we are justified in revealing - for the reason we will state in a moment... it would have revealed him as the illegitimate son of a Scotch servant girl!"

In his diary, Ramsay MacDonald recorded his reaction to the article. "On the day when the paper with the attack was published, I was travelling from Lossiemouth to London in the company as far as Edinburgh with the Dowager Countess De La Warr, Lady Margaret Sackville and their maid... I saw the maid had John Bull in her hand. Sitting in the train, I took it from her and read the disgusting article. From Aberdeen to Edinburgh, I spent hours of the most terrible mental pain.... Never before did I know that I had been registered under the name of Ramsay, and cannot understand it now. From my earliest years my name has been entered upon lists, like the school register, etc. as MacDonald. My mother must have made a simple blunder or the registrar must have made a clerical error."

MacDonald received many letters of support, including this one: "For your villainy and treason you ought to be shot and I would gladly do my country service by shooting you. I hate you and your vile opinions - as much as Bottomley does. But the assault he made on you last week was the meanest, rottenest lowdown dog's dirty action that ever disgraced journalism."

Lord Northcliffe also employed Bottomley to write a weekly column for The Sunday Pictorial. It is claimed that this alone earned him nearly £8,000 a year. In one of his articles under the heading: "A Million Coloured Troops: Act of Madness Not to Launch Them Against the Huns" he urged the government to mobilize the British Empire. He also wrote stories about German atrocities and suggested that the British Army should respond with their own "frightfulness".

In 1916 Bottomley helped Noel Pemberton Billing, get elected as the independent MP at the East Hertfordshire by-election. Billing was also the editor of The Imperialist. Both men used their newspapers to claim the existence of a secret society called the Unseen Hand. Bottomley even claimed that this group was responsible for the death of Lord Kitchener. Other supporters of this campaign included Lord Northcliffe (the owner of The Times and The Daily Mail), Leo Maxse (the editor of The National Review), the journalist, Arnold Henry White (the author of The Hidden Hand) and Ellis Powell (the editor of the Financial News). Bottomley claimed that members of the Unseen Hand were working behind the scenes to obtain a peace agreement with Germany.

As Ernest Sackville Turner, the author of Dear Old Blighty (1980) has pointed out: "One of the great delusions of the war was that there existed an Unseen (or Hidden, or Invisible) Hand, a pro-German influence which perennially strove to paralyse the nation's will and to set its most heroic efforts at naught... As defeat seemed to loom, as French military morale broke and Russia made her separate peace, more and more were ready to believe that the Unseen Hand stood for a confederacy of evil men, taking their orders from Berlin, dedicated to the downfall of Britain by subversion of the military, the Cabinet, the Civil Service and the City; and working not only through spiritualists, whores and homosexuals."

According to A. J. A. Morris: "His (Bottomley) patriotic appeals were barely disguised music-hall turns. The praise he received served to feed his latent megalomania. His political ambitions had always tended towards fantasy so that when, in December 1916, Lloyd George became prime minister Bottomley declared that he was ready to serve his country in some official capacity or other. He did not seem to realize that he was indelibly associated with dishonesty. Just as the blatant vulgarity of his writing in John Bull shamed journalism, so his speeches, with their ignominious appeals for sacrifice, degraded public life."

A.J.P. Taylor claimed that Bottomley made £78,000 from his "recruiting" and "patriotic" meetings. He used this money to pay off his debts and in the 1918 General Election he was returned as the independent MP for Hackney South. Soon afterwards stories began circulating about Bottomley's corrupt activities. This included his highly successful Victory Bond Club that he ran via John Bull Magazine. This scheme involved buying government Victory Bonds. It was claimed that he had corruptedly obtained over £900,000 in this way.

Bottomley was a strong critic of the Russian Revolution. In 1918 he became convinced that the journalist, Arthur Ransome, was a Soviet spy. In reality, Ransome was working for MI6. When he heard that he intended publishing a story on this in the John Bull Magazine Ransome immediately contacted his spymaster in Russia, Robert Bruce Lockhart, and told him that Bottomley intended to describe him as a "paid agent of the Bolsheviks" and asked him for help. He pointed out that he had been asked by Sir George Buchanan to be "an intermediary to ask Trotsky certain questions, my attempts to get into as close touch as possible with the Soviet people have had the full approval of the British authorities on the spot. I have never taken a single step without first getting their approval."

Ransome went onto argue that he was under orders to provide pro-Bolshevik reports: "As for my attitude towards (the Bolsheviks), please remember that you yourself suppressed a telegram I wrote on the grounds that its criticism of them would have put an end to my good relations with them and so have prevented my further usefulness. Altogether, it will be very much too much of a good thing if, after having worked as I have, and been as useful as I possibly could, I am now to be attacked in such a way that I cannot defend myself except by a highly undesirable exposition (to persons who have no right to know) of what, though not officially secret service work (because I was unpaid) amounted to the same thing." Lockhart contacted Bottomley and the article was never published.

In March 1922 he was charged with fraud. Tried before Mr Justice Salter at the Old Bailey, Bottomley was found guilty on twenty-three out of twenty-four counts and sentenced to seven years' penal servitude. His legal appeal was rejected and he was expelled from the House of Commons. He was released from Maidstone Prison in July 1927 after serving five years.

Bottomley launched a new journal, John Blunt. He also went on a speaking tours. However, he was unable to overcome his image as a swindler and both ventures ended in failure. His biographer, A. J. A. Morris, has pointed out: "He cut a pathetic figure and, a broken old man, he stumbled into obscurity. In 1930 his wife died and his daughter emigrated to South Africa. Of his former friends and acolytes all deserted him except Peggy Primrose, who shared her home with him."

Horatio Bottomley died of a stroke at the Middlesex Hospital, London on 26th May 1933.