The deal can be worth up to $76 million and includes $40 million guaranteed, the source said.
"It was kind of like a no-brainer and I'm glad it worked out," Golladay told reporters Saturday evening.
It didn't happen without a visit first. The Giants had questions for Golladay about the way his tenure in Detroit ended -- he had a shaky relationship with fired coach Matt Patricia -- and the hip injury that forced him to miss the final nine games of the 2020 season. He eased their concerns during meetings that lasted all day Friday, sources told ESPN.
Golladay remained in New York after the visit ended, while he passed one last medical hurdle and the final details of the massive deal were negotiated, sources said. It allowed him to sign at his preferred landing spot and gave the Giants -- most notably quarterback Daniel Jones -- the No. 1 receiver they desperately needed.
"Just the pieces on offense," Golladay said of what made the Giants so attractive. "Those guys actually kind of reached out to me and I liked the vision that coach Joe Judge had and [offensive coordinator] Jason Garrett, as far as the offense, and I was all the way in."
Jones was among the players who served as a recruiter. Safety Jabrill Peppers also reportedly had dinner with Golladay on Friday night.
"[Jones] reached out," Golladay said. "He just said how good of a player that he thought I was and I pretty much said the same thing about him.
"He also just said, you know, 'We're trying to do something great here,' and that's what I'm all about."
Jones said that when he spoke to Golladay, "he was interested in the culture we have in the building and the mindset of the team.
"I think he had heard it from coaches but wanted to hear how we saw it as players and how much we believed in it. I think finding the right fit in that sense was important to him. I can't wait to get out on the field and get to work with him."
Golladay emerged as the Lions' top receiving option the past three seasons, earning a Pro Bowl berth in 2019, when he amassed 1,190 yards and 11 touchdowns. He had hoped to improve on that in 2020, but hamstring and hip injuries limited him to five games and just 20 catches for 338 yards and two touchdowns.
A third-round pick by the Lions out of Northern Illinois in 2017, Golladay played in 47 games for Detroit, making 183 catches for 3,068 yards and 21 touchdowns. His ability to make contested catches down the field is something the Giants needed.
New York made it a priority to add playmakers this offseason and viewed Golladay as the only true No. 1 receiver on the market, according to a source.
"This team is going to get a competitor, a guy who's going to come in, work, he's going to try to push other guys and have fun with it," Golladay said. "I want to have fun while I'm doing this; that's what I'm doing it for. Just a playmaker."
Golladay, 27, reiterated in December that his preference would be to remain in Detroit. Of course, this was also before the trade of Matthew Stafford to the Los Angeles Rams and the hiring of new coach Dan Campbell and general manager Brad Holmes. However, Golladay did say then that his decision could be influenced by what the offense looked like -- and if Stafford was with Detroit.
"They drafted me here, so I just want to show my loyalty," Golladay said at the time. "They believed in me. If a contract [with the Lions] ... doesn't work out, it doesn't work out, you know. Then I go somewhere else and just ball out and play."
ESPN's Michael Rothstein contributed to this report.