Thomas Addis Emmet, Irish and American lawyer and politician, is born in the Hammond’s Marsh area of Cork, County Cork, on April 24, 1764. He is a senior member of the revolutionary republican group Society of United Irishmen in the 1790s and Attorney General of New York 1812–1813.

Emmet is a son of Dr. Robert Emmet from County Tipperary (later to become State Physician of Ireland) and Elizabeth Mason of County Kerry, both of whose portraits are today displayed at Cork’s Crawford Art Gallery. He is the elder brother of Robert Emmet, who is executed for leading the Irish Rebellion of 1803, becoming one of Ireland’s most famous republican martyrs. His sister, Mary Anne Holmes, holds similar political beliefs.

Emmet is educated at Trinity College, Dublin and is a member of the committee of the College Historical Society. He later studies medicine at the University of Edinburgh and is a pupil of Dugald Stewart in philosophy. After visiting the chief medical schools on the continent, he returns to Ireland in 1788. However, the sudden death of his elder brother, Christopher Temple Emmet (1761–1788), a student of great distinction, induces him to follow the advice of Sir James Mackintosh to forsake medicine for the law as a profession.

Emmet is a man of liberal political sympathies and becomes involved with a campaign to extend the democratic franchise for the Irish Parliament and to end discrimination against Catholics. He is called to the Irish bar in 1790 and quickly obtains a practice, principally as counsel for prisoners charged with political offenses. He also becomes the legal adviser of the Society of the United Irishmen.

When the Dublin Corporation issues a declaration of support of the Protestant Ascendancy in 1792, the response of the United Irishmen is their nonsectarian manifesto which is largely drawn up by Emmet. In 1795 he formally takes the oath of the United Irishmen, becoming secretary in the same year and a member of the executive in 1797. As by this time the United Irishmen had been declared illegal and driven underground, any efforts at peaceful reform of government and Catholic emancipation in Ireland are abandoned as futile, and their goal is now the creation of a non-sectarian Irish republic, independent from Britain and to be achieved by armed rebellion. Although Emmet supports this policy, he believes that the rebellion should not commence until French aid has arrived, differing from more radical members such as Lord Edward FitzGerald.

British intelligence infiltrates the United Irishmen and manages to arrest most of their leaders on the eve of the rebellion. Though not among those taken at the house of Oliver Bond on March 12, 1798, Emmet is arrested about the same time, and is one of the leaders imprisoned initially at Kilmainham Gaol and later in Scotland at Fort George until 1802. Upon his release he goes to Brussels where he is visited by his brother Robert in October 1802 and is informed of the preparations for a fresh rising in Ireland in conjunction with French aid. However, at that stage France and Britain are briefly at peace, and the Emmets’ pleas for help are turned down by Napoleon.

Emmet receives news of the failure of his brother’s rising in July 1803 in Paris, where he is in communication with Napoleon Bonaparte. He then emigrates to the United States and joins the New York bar where he obtains a lucrative practice.

After the death of Matthias B. Hildreth, Emmet is appointed New York State Attorney General in August 1812, but is removed from office in February 1813 when the opposing Federalist Party obtains a majority in the Council of Appointment.

Emmet’s abilities and successes become so acclaimed, and his services so requested that he becomes one of the most respected attorneys in the nation, with United States Supreme Court Justice Joseph Story declaring him to be “the favourite counsellor of New York.” He argues the case for Aaron Ogden in the landmark United States Supreme Court case of Gibbons v. Ogden, 22 U.S. 1 (1824) relating to the Commerce and Supremacy clauses of the United States Constitution.

Emmet dies on November 14, 1827, while conducting a case in court regarding the estate of Robert Richard Randall, the founder of Sailors’ Snug Harbor, a home for needy seamen in Staten Island, New York. He is buried in St. Mark’s Church in-the-Bowery churchyard in the East Village, New York City, where a large white marble monument marks his grave.