He left school at 12 and studied at the Dublin Metropolitan School of Art, alongside Augustus John (with whom he was to set up a short-lived art school in Chelsea) and Wyndham Lewis. His early cartoons were rejected by Punch, and he took a part-time teaching post at the Dublin School of Art (1902-1914) while exhibiting his paintings. During the First World War, he served in the army in 1916, and as an Official War Artist in 1917-1919. He drew widely admired caricatures of participants at the Paris Peace Conference. He was knighted in 1918.