Thomas William Mark Ashby OBE (23 August 1895 – 26 September 1957) was a New Zealand local body administrator and Mayor of Auckland City from 1956 to 1957. He was Auckland Town Clerk (in charge of the Auckland City Council) between 1944 and 1955, and secretary of the committee for the 1950 British Empire Games at Auckland.
In November 1956, he defeated the previous mayor John Luxford. Luxford had claimed waste (wasteful expenditure) inside the council in his 1953 campaign, but (though initiating a number of reforms) had not been successful in chairing the council.
Ashby died part-way through his term on 23 September 1957, aged 62 years, and was replaced by Keith Buttle in a by-election in November 1957.
Born in Auckland, Ashby was educated at Te Aroha High School, and at Victoria and Auckland Universities. He was a solicitor, and served in the Army in the First World War. In the 1951 King's Birthday Honours, Ashby was appointed an Officer of the Order of the British Empire for municipal services.