Born in Loanhead, Midlothian, MacTaggart was the grandson of the artist William McTaggart, the leading Scottish landscape painter of his period. MacTaggart studied at Edinburgh College of Art from 1918 to 1921, returning there in 1933 to teach until 1958. He painted landscapes and still lifes and was much influenced by the work of Edvard Munch and French artists such as Georges Rouault, whose use of colour to express emotions particularly inspired him. MacTaggart was President of the Royal Scottish Academy from 1959 to 1964.