It was an encounter in 1765 with Jonathan Strong, a teenage slave owned by the barrister David Lisle, which sparked Sharp’s outrage at the treatment of fellow human beings. Strong had been seriously injured by Lisle and was waiting to receive treatment from Sharp’s older brother William, a well-known surgeon, when Sharp happened to be visiting. Two years later, Lisle had Strong arrested as a run-away and had sold him to a slave trader. Sharp was contacted by the imprisoned young man and took up his case, inspiring him to research the law on British civil liberties and the legality of slavery.
In 1769, this resulted in Sharp’s first work on the inhumanity of slavery in A representation of the injustice and dangerous tendency of tolerating slavery. In it, he set out his thoughts on the legal status of slavery in Britain, using legal and historical documents to condemn the practice. In 1772, Sharp wrote an Appendix to the Representation in response to the Somerset case, in which he argued that any slave setting foot in England should become a free person.