The Scotland lock, 25, joined last summer from Edinburgh Gunners to link up with Glasgow head coach Sean Lineen.
Al said: "I'm really enjoying my rugby with Glasgow. It looks like we're going places because we have a good squad of players."
Lineen said Al's contract extension was great news for the club and Scotland fans.
Ally captained Warriors to 15 wins last season and a place in the knock-out stages of the European Challenge Cup.
He said: "I'm originally a Glasgow guy, so I'm glad to have signed for a longer period of time and to be part of this very optimistic club."
Lineen added: "There's no doubt he will play a major part with the Scotland national team in the future and it's exciting he's shown commitment to stay with Warriors because he's well respected and is developing into a world-class performer."