The talismanic skipper handed his side a huge boost on the eve of the first leg of their 1872 Cup derby bust up with Edinburgh at Scotstoun tonight by signing until at least May 2015.
The deal also offers the 31-year-old former Scotland captain the chance to move to an ambassadorial role with Scottish Rugby and the Warriors at the end of that two-year period.
A delighted Kellock said: "It's a privilege to play for Glasgow Warriors and I'm honoured to be captain.
"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 rugby in Glasgow."
Warriors head coach Gregor Townsend said: "Big Al embodies what the Warriors are all about and he will be one of the key drivers of our success.
"He 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 line-out forwards in the game right now and has been a major part of our strong scrummaging displays this year.'