The 19-year-old will link up with the Black Cats' U21 side from July 1.
Watmore featured regularly for Altrincham in the Conference North last season and scored 14 goals in 29 starts.
Academy manager Ged McNamee told Sunderland's official website: "We are pleased to welcome Duncan to the club and wish him the best of luck."
Source: Sunderland-Mad
Source: FOOTYMAD
