He was the second son of William Selwyn, treasurer of Lincoln's Inn in 1793, by Frances Elizabeth, daughter of John Dod of Woodford, Essex.
Soon after the marriage of Queen Victoria, Selwyn was chosen to assist Albert, Prince Consort in his legal studies.
A valetudinarian in later life, he lived in retirement at Pagoda House, Kew Road, Richmond, Surrey, an estate inherited from his father in 1817.
[2] Selwyn collaborated with George Maule in Reports of Cases argued and determined in the Court of King's Bench, London, 1814, 2 vols.
A successful work, its 13th edition, by David Keane, Q.C., and Charles T. Smith, judge of the Cape of Good Hope, appeared in 1869.