Marcus Leslie Hancock (March 10, 1892 – December 2, 1977) was an English-born horticulturist and politician in Ontario, Canada. He represented Wellington South in the Legislative Assembly of Ontario from 1943 to 1945 as a Co-operative Commonwealth Federation (CCF) member. He was known as a breeder of rhododendrons. In 1972, Hancock founded the Rhododendron Society of Canada. He died of heart failure at the age of 85. The Leslie Hancock Garden at the Montreal Botanical Garden was named in his honour. His son was urban planner Macklin Leslie Hancock.