Diehl, who had four years left on the extension that he signed in 2005, will earn $31 million under terms of the new deal.
The extension was worked out over the past month, Peter Schaffer, Diehl's agent said in a telephone interview.
"I think the Giants, in terms of organizations in the NFL, have a great history of treating their players fairly," Schaffer said.
Diehl has been a starter since being taken by the Giants in the fifth round of the 2003 draft. He has started 80 straight regular-season games.
The versatile lineman started 16 at right guard as a rookie and moved to right tackle in 2004. Over the next two seasons he started 30 games at left guard, but he also made one start at right tackle and one at left tackle. He moved to left tackle for the 2007 championship season.
"I'll play any position they put me on the field because I know that's what I need to do to help our football team win games," Diehl said Wednesday in an interview with NFL Sirius Radio.
"I just went out there and worked hard and played my position well and everything worked out with the Giants," he said. "And the best thing about it is I get to be a Giant for the rest of my career, which I wanted to do and be in the place that I started at and there's no better feeling than that."
Copyright 2008 by The Associated Press