Born in Leeds, Joseph Hardcastle was a merchant and evangelical activist. He was closely involved with the Clapham Sect of evangelicals and was appointed a director of the Sierra Leone Company – along with William Wilberforce, Henry Thornton and Thomas Clarkson – when it was founded in 1791 to protect Africans from slave traders. In opposition to the slave trade, Hardcastle displayed instruments of restraint and repression associated with the trade – handcuffs, shackles, thumbscrews, etc. – at his home in Surrey and worked to secure the parliamentary election of Wilberforce and other abolitionist evangelicals.
In 1795, he was a founder member of the London Missionary Society (LMS) and was elected its first treasurer, a position he held for more than twenty years. He was a generous supporter of the LMS and other evangelical and philanthropic causes, making rooms available at his counting house in the City for meetings and lending his own financial support. An accomplished negotiator and conciliator, Hardcastle’s work behind the scenes was invaluable to the operation of a number of organisations, not least the LMS.