The 25-year-old full-back, who has been at the Greene King IPA English Championship club Leeds Carnegie for three seasons, has become one of the most consistent performers in the second tier and now gets his chance in the top flight.
McColl learned his rugby at Dunfermline and was part of the Edinburgh Academy system. He earned Scotland Sevens and Under-20s caps in his teens.
He first headed down south to Doncaster Knights and his steady form for them encouraged Leeds to bring him in ahead of the 2011/12 season. Injuries have caused problems over the last three years, but when he has been available he has been one of the first names on the teamsheet at Headingly.
Gloucester's Director of Rugby Nigel Davies said: "He's somebody who stands out at Championship level. He's a very strong, very powerful runner from deep and hits good lines. As a result of playing in the Championship, he's gained a lot of experience and he's shown his quality."