His law giving bounties on the exportation of corn and imposing heavy taxes on its importation is noted by William Lecky as being largely responsible for making Ireland an arable instead of a pasture country.

It was said by his critics that his opposition to the Union was less political than personal: summoned to London for consultations, he found himself treated with contempt by the English officials he dealt with, who mocked his broad Irish accent and called him "Mister Spaker".

He ultimately refused to surrender the Speaker's mace, which was kept by his family[2] and is now on display in the Parliament House, Dublin (now the Bank of Ireland).

Foster was returned in 1801 to the new United Kingdom parliament as a member for County Louth, and from 1804 to 1806 was Irish Chancellor of the Exchequer under Pitt.

In 1821 he has created a peer of the United Kingdom as Baron Oriel, of Ferrard, in the County of Louth, and died on 23 August 1828.