The American War of Independence awakened much sympathy in Ulster, especially among the Presbyterians, who, being disqualified from holding office, desired a general emancipation including that of the Roman Catholics.

In 1778 the Irish parliament, under the influence of the reformist leader Henry Grattan, passed the Relief Act, removing some of the most oppressive disabilities. Meanwhile Irish Protestants, under the pretext of defending the country from the French, who had entered into an alliance with the Americans, had formed military associations of volunteers, with 80,000 members. Backed by this force they demanded legislative independence for Ireland, and as a result of Grattan's tireless campaigning the British parliament repealed Poynings' Law and much of the anti-Catholic legislation. 

Various societies were formed to carry on the agitation, and considerable lawlessness occurred, fostered by the so-called Ribbon Society. The reform of the British parliament in 1832 increased the number of Irish members from 100 to 105. More important, it gave the middle class more power, weakening the pro-English aristocracy. 

In 1838 a bill was passed converting the tithes into rent charges, to be paid by the landlords; as a result, agitation in connection with the Anglican Church ceased to be acute for a time. 

From 1845 to 1849 rent-racked Ireland suffered a disastrous famine resulting from the failure of the potato crop. The government, influenced by laissez-faire ideology, failed to provide adequate relief, and widespread tenant evictions compounded the problem. It has been estimated that 1 million died, mostly as a result of diseases caused by severe malnutrition; the west of the country was worst affected.

Concurrently, over 1 million people emigrated, especially to America and Canada.