Malcolm, who became a free agent on 1 November after rejecting Derbyshire's offer of a new contract, has signed a three-year deal.
"To make such a decision there are a hell of lot of things to be taken into consideration, such as my family," he said. "I have given it a lot of thought and I have decided to move to give me the extra motivation so I can win by England place back."
The fast bowler admitted that leaving Derbyshire, where he made his debut in 1984, was a big wrench. "I have had a great time at Derbyshire for 14 years and Derbyshire people have shown me a lot of affection, but you have to move on and I thought this was the best time to do it," he said.
Steve Coverdale, Northamptonshire's chief executive, said: "He is perhaps the most popular player in English cricket and is much admired as a cricketer and personality throughout the world. There has been enormous interest locally since it became known that we were in for him - it compares to that generated when we signed Dennis Lillee 10 years ago."
Malcolm will team up with his former Derbyshire team-mate Paul Taylor and overseas signing Paul Reiffel from Australia.Reuse content