Lobbe, 33, will complete his move in the summer and Northampton director of rugby Jim Mallinder said: "Ignacio is a player who has plenty of power, skill and leadership experience.
"He has played at the highest level for many years and knows how to win the biggest matches. This will be invaluable in the Premiership next season."
Lobbe has won 64 caps for Argentina, played in three World Cups and helped the Pumas to third place at last year's tournament in France.
In his four seasons at Sale, Lobbe won the European Challenge Cup in 2005 and the Premiership title in 2006.
"I've spoken with Jim and the coaches and I am really happy to move to Northampton," said Lobbe.
"It's a club with a lot of history in the Premiership and some great fans who go everywhere. When I was playing in France I went to see a quarter-final between Toulouse and Northampton and there were thousands of fans who were really loud.
"I've had an excellent four years at Sale, winning the Challenge Cup and the Premiership. But from July I will be totally focussed on my new challenge at Northampton.
"I really hope that we can have an excellent start to the new season and that I can help them get to being a top club in England."