Beckham joined the Giants as the No. 12 overall pick in the 2014 NFL Draft. Beckham made the Pro Bowl in his first three seasons, catching at least 90 passes for 1,300 yards and 10 scores in each of those campaigns.
He had 1,052 yards and six scores on 77 catches in 12 starts last season, while limited by a quad injury.
The Browns sent safety Jabrill Peppers, a first-round pick in the 2019 NFL Draft and a third-round pick in the 2019 NFL Draft to the Giants in exchange for Beckham.
"So many mixed emotions and feelings," Beckham wrote on Instagram. "This is all, a lot to process but it is reality. I don't know exactly what to say so just gotta keep it real and short. I want to thank the NY Giants organization for giving me an opportunity to do what God put me on this earth to do. I want to thank the organization and the owners for everything and especially giving me my first chance to be a part of the NFL."
"I want thank everyone in that building from the kitchen staff to my main man Jośe! I loved you guys dearly and always will. I gave you my all every Sunday. To the fans, some happy, some not, I just wanna thank you guys for making my experience in NY something I'll never forget! To the New Yorkers and real NYG fans ... you guys will always have a place in my heart, a beautiful city ... a beautiful place. Thank you for every last moment and experience. Without them, I wouldn't be exactly who I am today!"
Beckham's post was closing in on one million likes by Thursday afternoon. It featured comments from Tom Brady, Von Miller and several other celebrities and athletes. Los Angeles Lakers star LeBron James also liked the post.
"Well said," Brady wrote.
Beckham added another Instagram post Thursday morning, including a video of himself and new teammate Jarvis Landry doing football catching drills. The Pro Bowl wide receivers are longtime friends and were also teammates at LSU.