John Downey was born in Ireland, in 1799. He emigrated to the United States in 1818 and after settling in Ohio, found work in a drug store.
In 1848 gold was discovered on land owned by John Sutter in California. Downey joined the Gold Rush and later claimed that he only had $10 dollars when he arrived in California. After a short unsuccessful period as a miner, Downey moved to Los Angeles and with financial help provided by J. P. McFarland, opened his own drug store. This was a success and Downey was able to buy a large ranch.
Downey became active in the Democratic Party and in 1861 became governor of California. During the Civil War Downey helped raised troops for the Union Army but his own sympathies were with the Confederate Army.
After the war Downey became involved in real estate and in 1871 joined with I. W. Hellman to establish the Farmers and Merchants Bank. Two years later his company, the Downey Land Association, began building houses in East Los Angeles. He was also one of the founders of the Pioneer Oil Company and was the main figure behind the building of the Los Angeles Public Library.
On 29th January, 1883, Downey and his wife were on a train that crashed in the Techachapi Mountains. Downey's wife was killed and he suffered from nervous shock until his death in Los Angeles.