Born at Drumdowney, County Kilkenny and educated at Stonyhurst and TCD, Sheil supplemented the meagre income from his early legal career by writing plays which received mixed reviews. A campaigner for Catholic emancipation, he overcame his initial antipathy to Daniel O’Connell’s tactics to help him found the Catholic Association and secure victory in the Clare bye-election of 1828. Shiel was called to the Inner Bar in 1830 and was MP for Milborne Port, Somerset, County Louth, County Tipperary and Waterford successively, 1830–41. He enjoyed a series of sinecures, the last being British ambassador at Florence where he died.