As an ardent supporter of Lord Derby, he entered the lists against the sitting MP for Newry, the popular Presbyterian William Kirk, whom, against the odds, he expected to beat, and duly took the seat, sitting until 15 July 1865. Once in the Commons he gave Derby “a hearty but independent support”. He was succeeded in the seat by another Conservative, Arthur Innes.
Born at Newry in 1814, the youngest son of John Quinn of Newry and of Drum, County Monaghan, a merchant, and his wife, Mary, who was the daughter of the Vicar of Newry, the Reverend William Campbell. He married Sarah Jane Erskine, the daughter of the Rector of Kilbride in the diocese of Kilmore. They had four sons and three daughters. Two of their sons served in India, both with the Bengal Civil Service: John became Commissioner for Lucknow and Charles Commissioner for Bhaugalpore.
Peter Quinn was a Justice of the Peace in Counties Armagh and Down , served on the committee which issued the prospectus for the Newry, Armagh and Enniskillen Railway in the autumn of 1844 (the company was formed in 1845), was on the Board of the Newry Navigation Company, and was himself a merchant in Newry before becoming the land agent for sizeable estates in both County Down and Armagh.
Although he was thought to be a far stronger candidate than his predecessor, his opponent was as confident of retaining the seat as Quinn was of taking it. It was a hard fought contest, but the Conservatives had targeted Newry as one of four gains they hoped to make and Quinn did not disappoint them. His election in May 1859 was, not unexpectedly, the subject of an unsuccessful electoral petition and although he chose not to fight the seat again, Quinn had paved the way to another Conservative victory in 1865. However, Kirk persisted and was successful in 1868.
After his retirement from parliament, Quinn was elected in 1869 as a representative of the laity on the diocesan conference of Armagh, pledged to resist the disestablishment of the Church of Ireland.
He lived at The Agency, Drumbanagher, County Armagh.
His wife died on 5 January 1889 and Quinn died on 5 October 1894.