William Nugent Macnamara or M'Namara (c.1776 – 11 November 1856) was an Irish landowner and Member of Parliament.
He was the eldest son of Irish MP Francis Macnamara of Doolin and educated at a Dublin seminary. He entered the local militia as a captain of grenadiers, later gaining promotion to major. He was appointed High Sheriff of Clare for 1798-99, successfully keeping order during the Irish rebellion, and succeeded his father in 1815 as landlord of Doolin. He later acquired Ennistymon House by marriage.
He travelled about, including to the continent, between 1814 and 1816. When in Dublin in 1815 he acted as second to Daniel O'Connell (the Liberator) in his famous duel with John D'Esterre in which O'Connell wounded D'Esterre. In 1830 he was elected MP for Clare to take the place of O'Connell, who sat instead for Waterford. He was then re-elected in 1831, 1832 and 1847, retiring in 1852.
He died in 1856 and was buried in the family vault at Doolin. He had married Susannah, daughter and coheiress of Mathias Finucane of Lifford, with whom he had a son, Francis and four daughters. He was succeeded by Francis, an Army officer who had been an MP for Ennis.
He was described by a contemporary as "a Protestant in religion, a Catholic in politics, and a Milesian in descent".