Martha Wainwright (b. 1976 in Montreal, Quebec) is a Canadian singer and songwriter.

Daughter of Loudon Wainwright III and Kate McGarrigle, and the sister of Rufus Wainwright, she has frequently appeared on recordings by her family members, the McGarrigle Sisters and Family and has released several independent EPs. Wainwright released an independent cassette, Ground Floor, in 1997. The following year, her song "Year of the Dragon" appeared on The McGarrigle Hour, an album released by Kate & Anna McGarrigle.