Richard Sadleir (6 May 1794 – 6 March 1889) was an Irish-born Australian politician.
Despite an intention to enter the church, he went to sea with the Royal Navy in 1808, travelling widely before returning to Ireland a lieutenant in 1821.
In 1825 he migrated to New South Wales, and in 1829 he married Ann Cartwright.
From 1826 he was a settler in the Hunter River, and from 1829 he was a schoolmaster at the Male Orphan School in Liverpool.
In 1861 he was elected to the New South Wales Legislative Assembly for Lower Hunter, but he did not re-contest in 1864.