He was the 3rd son of Sir Edward Seymour, 4th Baronet (d.1708) of Berry Pomeroy in Devon, by his second wife Laetitia Popham (of which marriage he was the eldest son), a daughter of Alexander Popham (1605 – 1669), MP, of Littlecote in Wiltshire.
On 9 August 1683 his mother's childless cousin Edward Conway, 1st Earl of Conway (c.1623-1683), bequeathed him his extensive estates in Warwickshire and Lisburn, on condition that he should change his name to Seymour-Conway  and adopt the Conway arms. Considerable suspicion was aroused by this transaction, as it displaced Sir Arthur Rawdon, 2nd Baronet, Conway's nephew, from the succession. It was suspected that his father Sir Edward Seymour, 4th Baronet, had taken advantage of the Earl's senility to bring it about.
Death by duel
On 4 June 1699, during a drunken duel with Captain George Kirk of the Royal Horse Guards, Seymour-Conway was wounded in the neck. He succumbed to the effects of the wound two weeks later and on 18 June died in London.
- Debrett's Peerage, 1968, p.607, as borne by Seymour, Marquess of Hertford, eventual heir of Earl of Conway
- Lodge, Edmund (1832). Genealogy of the Existing British Peerage. Saunders and Otley. p. 187. Retrieved 2007-08-01.
- (firm), Oxford Journals (1881-01-08). "Rawdon Family". Notes and Queries. Oxford University Press (54): 27. Retrieved 2007-08-01.
- Hutton, Sarah (2004). Anne Conway: A Woman Philosopher. Cambridge University Press. p. 218. ISBN 0-521-83547-X. Retrieved 2007-08-01.
- Neill, Trevor (Winter 1995). "Lisburn Parliamentary Representatives in the 17th Century (1663-1700)". 9. Archived from the original on 2007-09-27. Retrieved 2007-08-01.
|Parliament of Ireland|
|Member of Parliament for Lisburn
With: Edward Harrison