Team President John Mara said the deal will keep Coughlin on the Giants' sidelines through 2014. His previous contract was to set expire at the end of the upcoming season.
"It has always been my belief that it is an honor and a privilege to be the head coach of the New York Giants," Coughlin said.
He has been New York's coach since 2004 and is second longest-tenured mentor in franchise history, trailing only Hall-of-Famer Steve Owen, who led the Giants for 24 years from 1930-53.
Coughlin took the team to Super Bowl titles last season and in 2007, defeating the New England Patriots both times.
"I wanted Tom as our head coach going all the way back to the early '90s," Mara said. "... In so many ways, Tom represents to me who and what the head coach of our franchise should be."