 The 19th and early 20th centuries saw the rise of modern Irish nationalism , primarily among the Roman Catholic population . The pre @-@ eminent Irish political figure after the Union was Daniel O 'Connell . He was elected as Member of Parliament for Ennis in a surprise result and despite being unable to take his seat as a Roman Catholic . O 'Connell spearheaded a vigorous campaign that was taken up by the Prime Minister , the Irish @-@ born soldier and statesman , the Duke of Wellington . <unk> the Catholic Relief Bill through Parliament , aided by future prime minister Robert Peel , Wellington prevailed upon a reluctant George IV to sign the Bill and proclaim it into law . George 's father had opposed the plan of the earlier Prime Minister , Pitt the Younger , to introduce such a bill following the Union of 1801 , fearing Catholic <unk> to be in conflict with the Act of Settlement 1701 . 
