The move comes as part of Northampton's plans to secure an understudy to England fly-half Paul Grayson, who could find himself selected for the England squad to travel to Australia for the Rugby World Cup in October, while the Premiership continues simultaneously.
The 25-year-old fly-half and fullback, who holds a British passport, had been linked with a number of other clubs including Bath, London Irish and newly-promoted Rotherham.
Head coach Wayne Smith said: “With Paul Grayson and Matt Dawson looking like they will both go out to the World Cup, goal-kicking became a major issue for us with Bruce Reihana being our only recognised kicker. Shane will provide quality back up to Bruce’s skills and will provide critical quality in the fly-half position that I remember only too well from his days with Queensland Reds.
Drahm told the British Press Association that although the decision had been a tough one to make, his gut feeling had always been with Northampton.
"Wayne Smith [Northampton coach] had a fair bit to do with my decision. He's one of the best coaches in the world, and the support set-up at Northampton is very impressive," he said.
"They are becoming top contenders for the Premiership, and it's been impressive looking at the facilities they have on offer."