Sweetman was an active United Irishman. He was a member of the Leinster directory of the revolutionary organisation, and some of the most important meetings of its executive committee took place at his brewery in Francis Street, Dublin. Shortly before the Irish Rebellion he was arrested with other leaders of the movement on 12 March 1798. Seeing that all hope of a successful insurrection was over, they entered into a compact with the government, by which, in consideration of a promise of the suspension of the executions of United Irishmen, they made a full disclosure of their objects and plans, without implicating individuals, before committees of the Lords and Commons. Sweetman was one of the group sent to Fort George in Scotland early in 1799. In June 1802 they were deported to Holland and set at liberty. After eighteen years of exile Sweetman was permitted to return to Ireland in 1820. He died in May 1826, and was buried at Swords, outside Dublin. He married, in 1784, Mary Atkinson, the daughter of a Dublin brewer.