Thomas Hamar Greenwood, 1st Viscount Greenwood, PC, KC (7 February 1870 – 10 September 1948), known as Sir Hamar Greenwood, Bt, between 1915 and 1929 and as The Lord Greenwood between 1929 and 1937, was a Canadian-born British lawyer and politician.
He served as the last Chief Secretary for Ireland between 1920 and 1922.
Both his sons died unmarried, so that the title of Viscount Greenwood became extinct in 2003.