The 28-year-old netminder posted a 32-22-4 record last season with four shutouts in 59 games. Lehtonen recorded a .922 save percentage and 2.33 goals-against average.
"Kari Lehtonen has worked extremely hard in his time with the Dallas Stars to establish himself as an elite goaltender in the NHL," general manager Joe Nieuwendyk said in a release.
"We believe that his best days as a goaltender are ahead and that his work ethic and leadership will help guide this team into a perennial Stanley Cup contender."
Lehtonen will be paid $5.9 million per year through the 2017-'18 season.
In eight NHL seasons with the Stars and Atlanta Thrashers, the six-foot-four, 217-pound Helsinki native has a 166-133-32 record with a 2.71 goals-against average and 21 shutouts.