The Scottish qualified back, who spent three weeks on trial at Scotstoun last season, will also play for Glasgow Hawks in the BT Premiership when he's not selected for the Warriors.
After being brought up in Christchurch in New Zealand, he has featured for Marist Albion Rugby Club and Canterbury age grade sides.
During that time he played against Warriors fly-half Finn Russell when he was over in New Zealand on the Macphail Scholarship in 2013.
Hagen qualifies for Scotland through his grandmother.
"I try and pride myself on a running and kicking game. Coming over here and training couldn't be more exciting.
"I'm currently living with Rory Clegg so I've been picking his brains about how the team works and what the plays are.
"Finn Russell played over in Christchurch when I was there, so it was good to see a familiar face when I arrived at Scotstoun.
"He is an outstanding player and someone who I want to learn from."
Glasgow Warriors head coach Gregor Townsend said: "Hagen came over to Glasgow in March and spent a few weeks training with us.
"He fitted in really well with our squad and also managed to play a game for Glasgow Hawks while he was here.
"We're delighted that he's accepted the opportunity to join us on a full-time basis.
"He was top points scorer in the Canterbury club competition last season and he has real variety in his kicking game.
"The step up to a full professional environment gives him a great opportunity to maximise his potential and work on all aspects of his game."
"They will support Hagen in adopting the Warriors culture and standards as well as providing additional opportunity to develop as a player."