At the 1705 English general election, he was returned as MP for Bossiney, and as commissioner for arranging the union with Scotland which he was largely instrumental in promoting.

Harcourt was appointed attorney-general in 1707, but resigned office in the following year when his friend Robert Harley, afterwards Earl of Oxford, was dismissed.

[1] Harcourt defended Sacheverell at the bar of the House of Lords in 1710, being then without a seat in Parliament; but in the same year was returned for Cardigan, and in September again became attorney-general.

In 1710 he had purchased the Nuneham Courtenay estate in Oxfordshire, but his usual place of residence continued to be at Cokethorpe near Stanton Harcourt, where he once received a state visit from Queen Anne.

On the accession of George I however, he was deprived of office and retired to Cokethorpe, where he enjoyed the society of men of letters, Swift, Pope, Prior and other famous writers being among his frequent guests.

Harcourt married first at St Marylebone on 18 October 1680 Rebecca Clarke (buried at Chipping Norton, Oxfordshire, 16 May 1687), daughter of the Rev.