In May 1788, Charles Fox precipitated the first parliamentary debate on the slave-trade. He denounced the "disgraceful traffic" which ought not to be regulated but destroyed. He was supported by Edmund Burke who warned MPs not to let committees of the privy council do their work for them. William Dolben described shipboard horrors of slaves chained hand and foot, stowed like "herrings in a barrel" and stricken with "putrid and fatal disorders" which infected crews as well. With the support of William Pitt, Samuel Whitbread, William Wilberforce, Charles Middleton and William Smith, Dolben put forward a bill to regulate conditions on board slave ships. The Dolben Act, passed 56 to 5 and received royal assent on 11th July.

William Dolben's biographer, Nigel Aston, has argued: "No cause was dearer to him than the abolition of slavery, or at least the improvement of conditions for black slaves being shipped to the West Indies on the middle passage. Despite opposition from the merchants of Bristol and Liverpool, with Pitt's support he successfully piloted a bill through the Commons in 1788 designed to limit the number of slaves allowed on a vessel in proportion to its tonnage (initially, for a trial period of a year). Dolben developed a close alliance in parliament with William Wilberforce on the slave trade. He supported in principle the series of abolition bills Wilberforce brought forward in the 1790s."

Suzanne Schwarz, the author of Slave Captain: The Career of James Irving in the Liverpool Slave Trade (1995), has pointed out: "The legislation, more widely referred to as the Dolben Act, specified that the master of a slave ship should have served on one previous voyage in that capacity, as chief mate or surgeon during two whole previous voyages or as chief or other mate in three voyages.... Under the terms of the Dolben Act ships could carry five slaves for every three tons burthen up to a maximum of 201 tons, and one slave for each remaining ton." The act also specified that the crew should be paid a bonus if less than 3% of the slaves died on the voyage.

Hugh Crow approved of the regulation of the slave-trade. However, he rejected the criticism of William Wilberforce: "His proposition... that badges should be worn by African captains, who toiled at the risk of their lives for the accommodation of our colonies, and that he and others might enjoy their ease at home, was impertinent as well as ungracious; and his regulation that captains should land their cargoes without losing a certain number of black slaves, was absolutely ridiculous. Not a word was said about the white slaves, the poor sailors; these might die without regret.... And with respect to the insinuation thrown out, in this country, that African captains sometimes threw their slaves overboard, it is unworthy of notice, for it goes to impute an absolute disregard of self interest, as well as of all humanity. In the African trade, as in all others, there were individuals bad as well as good, and it is but justice to discriminate, and not condemn the whole for the delinquencies of a few."