[1] From a Bristol merchant family who were slave owners in Jamaica, he was the eldest son of William Dickinson, also a Member of Parliament, and his wife Philippa Fuller, daughter of Stephen Fuller who was a London West India merchant and Jamaica agent.
[1][2] He was educated at Westminster School and Christ Church, Oxford where he matriculated in 1789, graduating with a B.A.
[1] Dickinson entered the House of Commons in 1796 for Ilchester, as a supporter of William Pitt the Younger.
In 1806 he was elected for Somerset, a seat he held until 1831, and moved his support generally to the Whig opposition.
[1] According to the Legacies of British Slave-Ownership at the University College London, Dickinson was awarded a payment as a slave trader in the aftermath of the Slavery Abolition Act 1833 with the Slave Compensation Act 1837.