A source told ESPN NFL Insider Adam Schefter that the deal is worth $5.55 million, with $3 million fully guaranteed.
Sources told Schefter that the Seahawks still plan to visit with free-agent running back Jamaal Charles on Wednesday.
Lacy, 26, appeared to be on track for a bounce-back season in 2016, averaging 5.1 yards per carry in the first five games, until a left ankle injury in Week 6 brought everything to a halt. He underwent surgery and was placed on injured reserve.
Seahawks coach Pete Carroll on Tuesday said Lacy, who was listed at 235 pounds last season and whose weight was an issue with the Packers in 2015, is rehabbing from the ankle injury and the Seahawks want his weight in the 240s.
"He's a big back. He's a big guy. Ain't nothing wrong with that," Carroll told The John Clayton Show on 710 ESPN Seattle. "But there will be a real concerted effort to make sure he's at his very best. This is a hard time for him because he's working some rehab right now, but he is well-aware of what our expectations and the standards that we're setting. We would not have done this if we didn't have a really clear understanding of how we're going to go forward.
"This is a big deal for him. It's a one-year contract for him. This is a chance for him to prove it and show where he is in the league and how he fits in and how he can work to secure a good future for him. And he knows all of that. Coming here is really something he's pumped up about because he knows how we see it, too. So we're going to get him in great shape. We're going to show him at his very best. There's a weight in there that's a really good spot for him that he's working toward. And we'll do a nice job with that."
Carroll made it clear after last season that fixing the Seahawks' running game was going to be an offseason priority after averaging just 3.83 yards per carry, which ranked 24th in the league. Seattle suffered a number of injuries, with 18 players getting at least one carry in 2016.
Lacy will join Thomas Rawls and C.J. Prosise in the Seahawks' backfield. Rawls had a great rookie year in 2015, but he battled through multiple injuries last season. The Seahawks view Prosise as more of a third-down back who can be used as a rusher and a receiver.
Carroll has said often that his preference is to go with multiple backs. Lacy is the favorite to get the bulk of the carries, but Rawls and Prosise will also factor in.
Lacy thanked Packers fans on Twitter while also expressing excitement about his new opportunity.
Thank you to the @packers organization for taking a chance on a kid from Gretna, LA. Life changing opportunity & am forever grateful 🙏🏿— Eddie Lacy (@Lil_Eazy_Ana_42) March 14, 2017
Lacy, a second-round pick from Alabama in 2013, posted back-to-back 1,100-yard seasons to start his pro career and was the NFL's Offensive Rookie of the Year in 2013.
However, his weight became an issue in 2015, when Green Bay coach Mike McCarthy said Lacy needed to come back in better shape after rushing for just 758 yards. After trimming down last offseason, he appeared to regain at least some of the weight he lost while working out with P90X founder Tony Horton, though he was still effective.
"That may have been a goal [playing at 235 pounds for the Packers], but he's a big man," Carroll told The John Clayton Show. "I want him big. I want him big and tough and strong, but I want him in the best shape so that he can run at his best and be durable and handle the load. ... So we have a real target for him. We'll be on it on a regular basis and we'll keep him in great shape."
Lacy's ankle injury was the impetus for the Packers to move receiver Ty Montgomery to running back full time last season.
ESPN's Sheil Kapadia and Rob Demovsky contributed to this report.