O’Connor was elected Member of Parliament for County Cork in 1832 as a supporter of Daniel O’Connell but lost his seat in 1835. In 1837 he founded a radical newspaper the Northern Star in England, and it was largely through his tireless energy and his ability as an orator that Chartism became a mass movement. After a term of imprisonment for seditious libel, he was elected Member of Parliament for Nottingham in 1847.