In 1920 he married Lilian Ryan, who became his model for a celebrated series of portraits. These were exhibited under the title Jane, followed by a Roman numeral that corresponded to the year of exhibition.[3] Other sitters included T. S. Eliot, Ralph Vaughan Williams, and Somerset Maugham, whom he painted 18 times.[4]
Maugham, a lifelong friend of Kelly, wrote an introduction to a catalogue (1950) of an exhibition of Kelly's work. Maugham regularly portrayed Kelly in his works, as Lionel Hillier in Cakes and Ale, as Frederick Lawson in Of Human Bondage and as O'Malley in His Excellency presenting him as "the young Irish painter called O'Malley", and dedicating Ashenden to him.[5]
He became a favourite painter of the Royal Family. During the Round Table Conferences in London, he encountered Shan princess Sao Ohn Nyunt. Struck by her grace and beauty, Kelly convinced her to pose for a series of portraits that would become some of his most celebrated works. Although he served as the court painter to the Royal Family during World War II, it was the 20 portraits of Sao Ohn Nyut that brought him unparalleled acclaim. These portraits, reproduced as posters, have sold over 50,000 copies and remain available to this day.[6]