The deal will allow him to continue to represent his hometown team until at least May 2015, with further options to keep playing or move into an ambassadorial role with Scottish Rugby and the Warriors at the end of that two year period.
Al said: "It's a privilege to play for Glasgow Warriors and I'm honoured to be captain of this club.
"Over the next three or four years I have one goal and that's to help this club win silverware. There is a strong squad and work ethic here and I want to be at the forefront of the push for success.
"I’m still keen to develop as a player and learn from the coaches at Glasgow. I'm still working hard at my game, still trying to improve and I have more to give to the Warriors.
"We have been shaping up over the last two or three seasons to do something special for the game in Scotland and compete with the best teams in Europe.
“Winning a trophy against these sides is something I desperately want to happen for the game of rugby in Glasgow."
Glasgow Warriors head coach, Gregor Townsend, said: "Alastair embodies what the Warriors are all about and he will be one of the key drivers of our success in the years to come.
“Al is an outstanding leader and ambassador for the club, but it’s his on-field performances that have earned him the reward of this contract extension.
“He is one of the best lineout forwards in the game right now and has been a major part of our strong scrummaging displays this year.
“Like any player in our squad there are areas he needs to keep working on to improve but I’ve been impressed with his low tackling and ball carrying this season. I’m delighted he has committed his future to the club."