In 1909 he went to the United States, where he remained except for a trip to Australia in 1913 and a visit to England in 1947. He served in the United States Navy in World War I and became an American citizen.
Henry Thomas competed as a bantamweight boxer for Great Britain at the 1908 London Olympics. The bantamweight division featured six boxers. Five were British; one was French. Here are Thomas' results from that boxing tournament:
Quarterfinal: defeated Frank McGurk (Great Britain) by decision
Final: defeated John Condon (Great Britain) by decision (won gold medal)