Thomas Arthur Lewis (21 September 1881 – 18 July 1923) was a Welsh school teacher, barrister and Liberal Party politician.
Lewis was the son of the Reverend J.M. Lewis, a Baptist minister from Cemaes, Pembrokeshire, and his wife Phoebe Griffiths. He attended the County School, Porth, and then at University College, Cardiff, where he took a degree in science In 1919 he married Marjorie Culross from Adelaide, South Australia, and they had one daughter.
After University, Lewis worked briefly as a school teacher but in 1910 he moved to London to become the private secretary to Freddie Guest who was at that time the Liberal MP for East Dorset. Guest would go on to become Chief Whip in the Coalition government of David Lloyd George. Guest later said that he talent-spotted Lewis and induced him to give up teaching and move to London to seek a political career.
Once in London, Lewis studied the law towards qualification as a barrister. Although he had what Guest described as a delicate constitution he joined the Officers' Training Corps at the Inns of Court in 1915 and was commissioned in April 1916. He served in Salonika from 1916–18 and achieved the rank of Lieutenant. He resumed his law career on return to Britain and was called to the Bar by the Middle Temple in 1919.