| Honorific-Prefix: | Lieutenant Colonel |
| Sir William Leggatt | |
| Constituency Am: | Mornington |
| Assembly: | Victorian Legislative |
| Term Start: | 8 November 1947 |
| Term End: | 3 February 1956 |
| Predecessor: | Alfred Kirton |
| Successor: | Roberts Dunstan |
| Birth Date: | 23 December 1894 |
| Birth Place: | Malekula, New Hebrides |
| Death Place: | Heidelberg, Victoria, Australia |
| Restingplace: | Springvale Botanical Cemetery |
| Nationality: | Australian |
| Party: | Liberal and Country Party |
| Alma Mater: | University of Melbourne |
| Profession: | Barrister and solicitor |
| Allegiance: | Australia |
| Branch: | Australian Imperial Force Citizens Military Force |
| Serviceyears: | 1915–1919 1934–1946 |
| Rank: | Lieutenant Colonel |
| Commands: | Sparrow Force 2/40th Battalion |
| Battles: | First World War Second World War |
| Mawards: | Knight Bachelor Distinguished Service Order Military Cross Mentioned in Despatches (2) |
Sir William Watt Leggatt, (23 December 1894 – 27 November 1968) was an Australian soldier, lawyer and politician. He served as commanding officer of the 2/40th Battalion and later Sparrow Force during the Second World War, fighting in Timor against the Japanese invasion in 1942. He was captured by the Japanese and sent to Changi Prison in Singapore. Following the war, he was based in Melbourne in charge of war crimes investigation until 1946. In 1948 he was elected to the Victorian parliament. He died in 1968 and was accorded a state funeral.