His most notable works are the monument to Sir Thomas Picton in St Paul's Cathedral, and a statue of the Duke of Kent in Park Crescent, Portland Place.
[5] In London he became an assistant to Joseph Nollekens, carrying out the carving of many of his major works, including the statue of William Pitt for the Senate House at Cambridge (1809),[6] and producing copies of busts.
[5] In his biography of Nollekens, JT Smith used the relatively small payments received by Gahagan as evidence of the older sculptor's miserliness.
[11]He may also have been responsible for the figures of Isis and Osiris made for the front of William Bullock's Egyptian Hall in Piccadilly (1811),[6][14] now in the collection of the Museum of London, although some sources attribute these to his father, Lawrence.
[2] Several other members of his family, apart from his father and brothers became sculptors and modellers;[6] they included his nephew Lucius Gahagan, and his niece, Sarah.