The Giants confirmed the length of the extension, which was described as "lucrative," but did not note the actual figure.
Josina Anderson of ESPN first broke news of the agreement, noting that $65 million is guaranteed.
Beckham's teammate, Roger Lewis, shared a video of him dancing in the locker room after the deal was done:
"Honestly, I don't even know how to explain it," Beckham said in the team's release. "I don't know if it's a relief, I don't know – it's a combination of everything. You've worked all your life to get to this point and it's finally here. I have to thank Mr. Mara, Steve Tisch, Mr. Gettleman, coach (Pat) Shurmur, Eli (Manning), all the guys I played with in the past years. Everybody was really a part of this—my mom, my dad, my family, everybody who was supporting me through this. It's just such an amazing feeling, I can't even explain. Most importantly, I have to thank God for being able to put me back together mentally, physically, spiritually. This is just truly amazing; I don't even know the right words to describe.
"It was just a time of patience and waiting and I knew that it would get done, it just was a matter of when and I'm just so happy that it is finally done now."
Beckham skipped the Giants' organized team activities last May, but he didn't immediately announce why. ESPN's Adam Schefter later reported his absence from the voluntary workouts was "directly related" to his "desire for a new contract."
Giants co-owner John Mara made the team's intentions clear during a town hall-style event with fans last June, per Art Stapleton of The Record.
"Obviously, we want him to be a Giant for the rest of his career," Mara said.
The feeling was mutual. Beckham, a three-time Pro Bowl selection and the 2014 Offensive Rookie of the Year, previously discussed his desire to remain in New York for a "long time."
In July 2016, Kaylee Pofahl and Paul Schwartz of the New York Post passed along comments the wideout made during a football camp in New Jersey aimed toward kids.
"I wanted to do one back home [in New Orleans] as well, but this is my first one, so New York's gonna be my home for a long time, so I felt like might as well start here and then go back home," Beckham said. "Kinda see how this went, and obviously it turned out great, so looking forward to doing many more."
As always, it came down to making the finances work for both sides. Beckham had a cap hit of only $3.3 million during the 2017 season, according to Spotrac, which came to a premature end when he suffered a broken ankle in early October.
Across his first 43 career games, Beckham tallied 288 catches for 4,122 yards and 35 touchdowns. That includes a career-high 101 grabs for 1,367 yards and 10 scores during the 2016 campaign. His catch total ranked third in the league that season behind Larry Fitzgerald and Antonio Brown.
Beckham caught 25 passes for 302 yards and three TDs in four games before he suffered his season-ending injury in 2017.
His on-field success hasn't been without some off-field controversy, though. The 25-year-old LSU product came under intense scrutiny after he joined a group of teammates on a boat trip the week before the team's 38-13 playoff loss to the Green Bay Packers in January 2017.
Regardless, working out a new contract with Beckham was always a no-brainer for the Giants. He's quickly developed into one of the NFL's most dynamic playmakers, highlighted by his trademark one-handed catches, and he would have been nearly impossible to replace.
Beckham is entering what should be his prime, so he's likely to provide New York's offense with plenty of bang for the buck moving forward.