In 1796 he was appointed acting Town Major of Dublin, confirmed in it in 1798. He was responsible for the arrest of Irish revolutionariesLord Edward FitzGerald, Thomas Russell and Robert Emmet. In 1802 he was mulcted £150 damages, and costs, for the assault and false imprisonment of John Hevey. His lawyer in this case referred to his "very great exertions and laudable efforts" to crush the Irish Rebellion of 1798. The opposing lawyer, John Philpot Curran, told a long tale of a grudge held by Sirr against Mr Hevey, the latter a prosperous businessman and a Yeoman volunteer against the Rebellion, who had happened to be in court during a treason case brought by Sirr. Hevey had recognised the witness for the prosecution, described him in court "a man of infamous character", and convinced the jury that no credit was due to the witness. The treason case collapsed. Sirr and his colleague had then subjected Hevey to wrongful arrest, imprisonment incommunicado, extortion of goods and money, and condemnation to hanging. Curran implied that these techniques were typical of the methods used by Sirr and by others to suppress the Rebellion.
Later life
In 1808 the Dublin police was re-organised and his post was abolished, but he was allowed to retain the title. Niles' Register of 24 March 1821 remarks that "Several persons have been arrested at a public house in Dublin, by major Sirr, charged with being engaged in a treasonable meeting, and committed to prison... We thought that this old sinner, given to eternal infamy by the eloquence of Curran, had gonehome". He founded the Irish Society for Promoting Scriptural Education in the Irish Language. Sirr was an avid collector of documents and curios. He sold McCormac's Cross and other valuable antiquities in exchange for second-rate copied paintings. The remains were given by his older son, Joseph to Trinity College, Dublin at some time between 1841 and 1843. It now forms the Sirr Collection of the Trinity College Library, Dublin He was buried in the churchyard of St. Werburgh's Church, while his victim, Lord Edward FitzGerald, was buried in the vaults of the same church.
Fictional representation
In many later Irish nationalist plays Sirr was portrayed as a generic melodramatic villain. James Joyce used him as the "type of the Irish turncoat" in Dubliners. In Ivy Day in the Committee Room a character remarks: "There's a lineal descendant of Major Sirr for you if you like! O, the heart's blood of a patriot! That's a fellow now that'd sell his country for fourpence—ay—and go down on his bended knees and thank the Almighty Christ he had a country to sell." In Master and Commander by Patrick O'Brian, a character refers to the Rebellion having spawned "a vile race of informers and things like Major Sirr".
