"I see myself being a great complement to Calvin and … him being a great complement to myself," Tate told reporters during an introductory news conference. "There’s so many things you can do with a player like myself and Calvin that it’s going to be hard to stop us."
The deal is worth around $31 million with about $13 million guaranteed.
Tate confirmed his decision on Twitter shortly after word leaked out, saying, "Wow I’m officially a Detroit #Lion. Extremely excited about the opportunity to grow with this organization."
He then added: "However Seattle I am extremely thankful for the support and love the city has given me over the past 4 years. It’s tough to leave such a great place.
"I appreciate everything the city, coaches, and teammates have done for me. I will always value how great Seattle was to me."
Tate was clearly the Lions’ primary target this offseason, just like running back Reggie Bush was a year ago.
Tate, who led the Seahawks last season with 64 receptions for 898 yards, flew into Detroit hours after free agency began Tuesday.
Wow I'm officially a Detroit #Lion. Extremely excited about the opportunity to grow with this organization.
As with Bush, the Lions didn’t let him get away without a finalizing a deal.
Tate had planned to fly out early Wednesday afternoon, but a major snowstorm forced him to stay an extra night.
It didn’t take too long for his agent to iron out the details on the agreement with the Lions, and Tate ended up taking part in the news conference at the team’s headquarters in Allen Park, Mich., late in the afternoon.
Tate was greatly appreciative of Lions vice chairman Bill Ford Jr. for meeting with him for about 15 minutes, just three days after Ford’s father, Lions owner William Clay Ford Sr., passed away.
"That meant a lot," Tate said. "I felt like I was wanted here."
Tate, 25, will give quarterback Matthew Stafford another valuable weapon while taking some of the load off of Johnson.
Johnson has been the only Detroit receiver with more than 39 receptions in each of the last two seasons.
Tate (5-foot-10, 202 pounds), who played in college at Notre Dame, will replace Nate Burleson as the Lions’ No. 2 receiver.
While Burleson, released a few weeks ago, has been injured the last two seasons and is nearing the end of his career, Tate is just entering his prime of his.
It’s an immediate upgrade for the Lions, and even more so for the future.
Over the last three seasons, Tate has dropped only five of 149 catchable passes — the lowest rate in the NFL, according to Pro Football Focus.
That’s a welcome addition for a team that led the NFL in dropped passes last season.
One of the attractions in coming to Detroit for Tate is the Lions’ pass-happy offense after playing in a run-first system in Seattle, where the defense got much of the attention.
A year ago, Bush was sold on the Lions because he knew with Johnson on the outside that he would have good opportunities in the run game against defenses that were focused on the pass.
Tate believes that he can benefit in a similar way by being paired with Johnson, who receives so much special attention from the secondary that other receivers often get single coverage.
The Lions are coming off disappointing 7-9 and 4-12 seasons since making the playoffs in 2011, but new coach Jim Caldwell has vowed that the "time is now" and that the team is in position to bounce back and win immediately.
Tate should fit in perfectly.
"I just feel like we’re close," he told reporters. "After looking at all the pieces and the plan, I feel like this organization is close.
"This is another city like Seattle that’s thriving for something great to happen."