William Forsyth QC (25 October 1812 – 26 December 1899) was a Scottish lawyer and ConservativeMember of Parliament (MP).
He was born at Greenock in Renfrewshire, son of Thomas Forsyth and Jean Campbell Hamilton. He died at Knightsbridge, Middlesex.
He was educated at Sherborne School and Trinity College, Cambridge, where he graduated B.A. in 1834. He was admitted at the Inner Temple in 1834 and called to the Bar in 1839. He became a Bencher in 1857, Queen's Counsel in 1857 and Treasurer in 1872. He worked on the Midland Circuit. He was Standing Counsel to Secretary of State for India 1859 to 1874. He was elected as MP for Cambridge at the 1865 general election but was unseated in April 1866, being disqualified as holding an office of profit under the Crown. He was later MP for Marylebone from 1874 to 1880. He wrote a number of books on historical and legal subjects, including History of Trial By Jury (1852), Life of Cicero (1864), The Novels and Novelists of the Eighteenth Century (1871) and Hannibal in Italy (1872). He was also editor of several magazines. Forsyth was a member of the Canterbury Association from 1 May 1848 to 22 April 1850, when he resigned. In 1849, the chief surveyor of the Canterbury Association, Joseph Thomas, named Lake Forsyth for him. His will probated at £18,667 in 1899.