Portrait of a lady, half-length, in a yellow dress and a white shawl, feigned oval

Little is known about Mosman's early years. It is probable that he was born in Aberdeen and he is known to have studied briefly in London, possibly under William Aikman, before visiting Rome between 1732 and 1735 where he was under the tutelage of Francesco Imperiali. Mosman's best known pictures, including Thomas, 9th Earl of Cassilis (Culzean Castle, National Trust), were executed in the 1740s when he was in Edinburgh. The following decade, he returned to Aberdeen where he painted local views and portraits and established a drawing school. He died near Aberdeen on 26 November 1771.