Coughlin, 69, announced Monday that he is stepping down as coach.
"I met with (Giants co-owners) John Mara and Steve Tisch this afternoon, and I informed them that it is in the best interest of the organization that I step down as head coach," Coughlin said in a statement. "I strongly believe the time is right for me and my family, and as I said, the Giants organization."
The Giants were 102-90 under Coughlin, but haven't made the playoffs in four seasons. In its last playoff appearance, the 2011 Giants beat the New England Patriots in Super Bowl XLVI.
"It has been an honor and a privilege to serve as head coach of the New York Football Giants. This is a not a sad occasion for me. I have spent 15 years with this organization as an assistant and head coach and was fortunate to be part of three Super Bowl winning teams. A Lombardi Trophy every five years is an achievement in which we all take great pride.
"Obviously, the past three years have not been what any of us expect, and as head coach, I accept the responsibility for those seasons.
Coughlin's team finished 6-10 this season and last season. Coughlin spent a dozen years with the Giants and eight years with the Jacksonville Jaguars, compiling a 170-150 career record. Coughlin coached teams won two conference titles and five division championships, with a .632 winning percentage.
"I think it has been evident these last 12 years here how much pride I take in representing this franchise," Coughlin said in the statement. "I am gratified and proud that we were able to deliver two more Lombardi trophies to the display case in our lobby during that time. That is a tribute to our players and staff, and it was truly fulfilling to be the leader of those teams.
"I appreciate the support of John and his family and Steve and his family, and of Jerry Reese and his staff. I think our organization is a great representation of what I mean when I talk about 'team'.
Coughlin has the second most wins for an active coach, trailing only New England's Bill Belichick's 223. Coughlin held a 12-7 career record in the playoffs.
"Finally, I would be remiss if I did not thank my wife Judy and our four children and their spouses and our 11 (soon to be 12) grandchildren. None of this would have been possible without their unconditional love and support."
Several somber Giants voiced concerns about the idea of losing Coughlin Monday, before the news broke.