A first cousin of the English politician Hugh Childers, he was a clerk in the House of Commons from 1895 to 1910, except for a period of service in the South African War. He resigned this position to devote himself to the cause of Irish Home Rule. In July 1914, at Howth, north of Dublin, he landed from his own yacht a cargo of rifles that he had purchased in Germany for the Irish revolutionary volunteers.

Despite his position on British rule in Ireland, Childers served the British in World War I as an intelligence and aerial-reconnaissance officer. But by the end of the war he supported a wholly independent Irish republic. In 1921 he was elected to the Dáil Éireann (Irish Assembly) as a Sinn Féin deputy from County Wicklow and became the Dáil's minister of propaganda. Later that year he was secretary to the Irish delegation to the Anglo-Irish treaty conference. Opposing the concessions that the Irish leaders Arthur Griffith and Michael Collins made to the British in signing the treaty (Dec. 6, 1921), Childers joined the Irish Republican Army (IRA), which resorted to civil war. Captured by Free State forces, Childers was court-martialed in Dublin on a charge of unauthorized possession of a revolver and was shot by a firing squad.

Childers was the author of The Riddle of the Sands (1903), a popular spy story involving an imaginary German raid on England.