A member of the Seymour family headed by the Duke of Somerset, Hertford was the eldest son of Francis Seymour-Conway, 1st Marquess of Hertford, and Lady Isabella Fitzroy, daughter of Charles FitzRoy, 2nd Duke of Grafton, born on 12 January 1743 in London.

[1] In 1766, he entered the British House of Commons as Member of Parliament for Lostwithiel, changing in 1768 to represent Orford until he succeeded his father in 1794.

In 1790, with Jones arguing that reform was impossible without Catholic Emancipaton, Hertford's nominees regained parliamentary control of the borough.

[4][5] Hertford was himself sympathetic to the case for Catholic "relief" (in May 1778 he declared himself strongly in favour of the repeal of the penal acts affecting Roman Catholics) and in "A Letter to the First Company of Belfast Volunteers", published in Dublin, 1782, he endorsed the case for Ireland's legislative independence.

He did not, however, embrace the call for parliamentary reform (abolition of the proprietary boroughs and a broader franchise) and he was averse to any further assertion of Irish independence.

[1] In 1829, he ordered MPs beholden to him to vote for the Roman Catholic Relief Act which finally removed the Protestant monopoly on Parliament.