Coughlin, 67, was entering the final year of a contract signed in June 2012. He announced the new deal at the NFL Combine in Indianapolis.
The Giants were 7-9 last season, the first losing season for Coughlin in since his first season in New York when the team went 6-10 in 2004.
In 10 years as the Giants' head coach, Coughlin is 90-70 with two Super Bowl championships. The win in Super Bowl XLVI after the 2011 season marks the only playoff season for the Giants since 2008.
Coughlin is the second-longest tenured coach in Giants' history behind Steve Owen, who led the team from 1930-53.
Coughlin first's head coaching position in the NFL was with the Jacksonville Jaguars from 1995-2002. His overall coaching record is 158-130 with a 12-7 record in the playoffs.