Sir Thomas Manly Deane (1851–1933) was an Irish architect, the son of Sir Thomas Newenham Deane and grandson of Sir Thomas Deane, who were also architects.
Born at Ferney House, Blackrock, Cork, on 8 June 1851, he was educated at Trinity College, Dublin, and travelled in France and Italy before joining his father's practice. Deane went into partnership with his father from 1884 till his father's death in 1899, when he joined Sir Aston Webb.
He designed three buildings of note in Dublin, Ireland. These are the National Museum and National Library on Kildare Street and also in the 1937 Reading Room in Trinity College Dublin.
He was knighted in 1911 and died in Wales on 3 February 1933.