The left-hander from Queensland has agreed a two-year playing contract and will succeed Kevin Curran as captain. David Ripley, the wicketkeeper, will be his deputy.
Hayden, 27, who made the last of his seven Test appearances for Australia in South Africa nearly two years ago, had a highly successful season with Hampshire in 1997. He scored 2,426 runs in all competitions, including 1,438 in the County Championship with four centuries.
Speaking from his home in Brisbane, Hayden said: ``I'm very excited about this. I enjoyed my summer with Hampshire and I just hope I can make a really good fist of it for Northants.''
He will team up with Bob Carter, the director of cricket, who said: ``I'm delighted Matthew is joining us. We spent a lot of time together in Brisbane last month and was impressed with his ideas and vision.''