The reigning American League batting champion and St. Paul, Minn., native will be paid $33 million over the life of the deal, the team said on its Web site.
"To know that I'll be playing in Minnesota for the next four years is a great feeling," the 23-year-old Mauer said. "Just to be able to be behind the plate when the new stadium opens is something that I'm really looking forward to."
The team is building a new facility which is scheduled to be ready by 2010.
In the 2006 season, Mauer became the first catcher to win an AL batting title, and the first catcher to lead the majors in hitting with a .347 average.
He had 13 home runs and 84 RBI, and was named to the AL All-Star team.