[1] Seymour was the third son of Francis Seymour-Conway, 1st Marquess of Hertford and Lady Isabella Fitzroy.
[3] Seymour-Conway was returned for two Parliamentary seats in 1771: Lisburn, in the Parliament of Ireland, and the family borough of Orford in the British House of Commons.
He left his Commons seat in 1790, the year that he and his brother Henry were granted, for life, the sinecures of joint prothonotary, clerk of the crown, filazer, and keeper of the declarations of the King's Bench in Ireland.
[citation needed] On 1 July 1807, Seymour, who owned a house in Portland Place, was sworn a Justice of the Peace for Middlesex.
He took an active role in civic affairs in London, and was for some time Director of the Poor for his parish of St Marylebone.
This included a particular interest in the care and treatment of the insane, culminating in his appointment in 1827 to the commission superintending the building of Hanwell Asylum and as a Metropolitan Commissioner in Lunacy in 1828.