Thomas spent most of his childhood within his father's plantation with himself attending the schools at New Orleans before graduating from Tulane University.

[1][2] After graduating from Tulane University, Lewis enrolled in the United States Military Academy on September 1, 1875, after securing his appointment.

He led the regiment at the Battle of San Juan Hill and the Siege of Santiago and was one of the first to receive news of the Spanish surrender from July 19 to August 16.

After the war, he was sent to Montauk, New York, in August 1898 before being transferred to Huntsville, Alabama, and returned to Cuba in February 1899 to command Companies E, F and G of the 2nd Cavalry Regiment.

[1][2] Lewis was placed on the United States Army Reserve on December 1, 1913, and was sent to the General Recruiting Service at Oklahoma City and New Orleans from 1913 and 1918.