Jackson did not practice with the Seahawks during the team's final day of minicamp.
Seattle head coach Pete Carroll said that Jackson will compete with Brady Quinn for the backup quarterback job behind Russell Wilson.
"I think it's a great boost for us in a competitive sense," Carroll said. "We thought of Tarvaris as a tremendously tough football player. And a competitive kid that battled for us. And we're a little better than we were in those days.
"So we bring him back with the thought that he'll make this a real competitive situation."
Jackson would appear to have an advantage over Quinn because of his familiarity with Seattle's players, along with six years playing under offensive coordinator Darrell Bevell's West Coast-based offensive system.
Jackson, 30, has a 17-17 record as a starter, throwing for 7,075 yards, 38 touchdowns and 35 interceptions. He has a career 59.4 completion percentage and a 77.7 career passer rating.
Jackson finished 7-7 in his only year as Seattle's starter in 2011, playing most of the year with a torn pectoral muscle.
However, Jackson finished 0-4 in late-game situations where he had a chance to lead the Seahawks to a win at the end of the contest - one of the reasons Seattle traded him to Buffalo for a seventh round selection in August of last year and started Wilson.
Buffalo released Jackson on June 10.
Quinn, 28, has a 4-16 record as a starter, throwing for 3,043 yards, 12 touchdowns and 17 interceptions. Quinn has a 53.8 career completion percentage, and a career 64.4 passer rating.
Carroll said bringing back Jackson was not a reflection on the way Quinn had performed during the team's offseason program.
"In the situation he's in, he's been next to perfect," Carroll said. "He has worked like crazy. He knows exactly what we're asking of him. He's a tremendous guy in the meeting rooms, on the practice field, and supporting Russell's efforts to figure it out. And he's competed really well. He's had a plenty of looks, and he's done a good job for us."
Seahawks wide receiver Doug Baldwin has an affinity for Jackson because of the success he had with the Alabama State product during his rookie season, leading the Seahawks in receptions two years ago.
"He's loved in the locker room because of what he did for us in 2011," Baldwin said. "He fought through injuries, and was able to put his best foot forward out on the field. And like I said, the guys in the locker room love him. And he's got unbelievable knowledge about the game."
--Asked about the possibility of Russell Wilson suffering a setback in his second season, Seahawks head coach Pete Carroll said his quarterback is up to the challenge.
"He had a great (rookie) year," Carroll said. "It'd be hard for anybody to come back and have a better year. It's a challenge in itself just to do that. That's just something that anybody who has a good season has to deal with. I think his mindset is excellent. And his preparation, his habits, his concern and his focus is excellent."
Wilson, who earned an invitation to the Pro Bowl as a surprise rookie starter for Seattle, echoed those sentiments.
"I don't even know those words," Wilson said when asked about the possibility of a sophomore slump. "I don't pay attention to it. I think the biggest thing is just focusing on tomorrow and focusing on the day - the rest of the day that I have and the next couple hours I have here."
Wilson's command of Seattle's offense was on display at the Seahawks' mandatory minicamp, as he expertly executed a Seattle offense that appeared in midseason form, with several pinpoint passes to receivers Golden Tate and Doug Baldwin, along with tight end Sean McGrath.
"The reads are coming a lot easier for all of us on offense," Baldwin said. "Russell's seeing us. He knows what we're capable of doing. And he's finding us in the holes that he didn't necessarily see last year just because we've got that rapport and chemistry growing now."
Even though the Seahawks will have five weeks until the beginning of training camp, tentatively scheduled for July 25, Russell doesn't plan on taking much time off to rest his mind and body.
Wilson says he doesn't need it.
"I'll rest later," he said. "You guys have got to remember I played two sports most of my life. It's one of those things where I've never had a break - ever - before this past offseason. My biggest thing is I like to have a lot of things on my plate."
And the driving force for Wilson and the rest of his teammates remains the thought that this year could be special.
"We have so much talent on this team, and we believe that we're capable of winning the Super Bowl - not only this year," Baldwin said. "That's just our belief. You wouldn't step out on the field if you didn't believe that."
With starter Marshawn Lynch a no-show at times during Seattle's offseason training program, younger running backs got an opportunity to show what they can do.
Seattle head coach Pete Carroll praised the improved play of reserve running back Robert Turbin. Seahawks quarterback Russell Wilson referred to the Utah State product as a starting-caliber runner.
Turbin did not practice the last two days of minicamp because of a sore foot. However, Carroll indicated that Turbin wanted to practice, but the team's training staff was holding him back.
"There's nothing that Robert can't do," Carroll said. "He can run the ball, he can catch the football, he's a really good pass protector, and he's a good special teams player also. We expect a tremendous amount out of Robert. He'll play regularly and we'll have no hesitation of putting him in the game in all situations."
This year's second-round selection Christine Michael also showed a quick burst through the hole and elusiveness out in the open field during minicamp.
But his next test will be how he runs when the defense can actually tackle him.
Carroll also praised sixth-round selection Spencer Ware, saying he's done a nice job learning both the tailback and fullback position.
"Spencer Ware has made a really good impression," Carroll said. "He came out here to play two positions and we didn't know if he could handle that, but he has. He can play fullback and tailback for us at this time.
"Just by the way he's demonstrated his savvy and instincts, and we know he's a real tough guy, we think he's going to be a very good special teams player. We can't tell that yet, we don't know because guys are learning, and that doesn't happen until we put the pads on. But we expect Spencer to be a big part of it."
Seahawks owner Paul Allen was out on the field watching minicamp workouts June 13. Allen spent time talking with former Seahawks quarterback and assistant coach Jim Zorn, along with Carroll and general manager John Schneider.
"It was good to see the owner out there today," Carroll said. "Mr. Allen came out and saw us work on the last day and it looked like he was having a good time, too. So we ended on a good note, and we'll come back five weeks from now or so and get cranking."
Running back Marshawn Lynch checked in at No. 24 on The NFL Network's Top 100 players of 2013, a distinction voted on by players from around the league. Lynch joins fellow teammates Richard Sherman (50), Russell Wilson (51), Earl Thomas (66), Percy Harvin (90) and Max Unger (95).
"His lean body mass has shifted some. But he still weighs 350 pounds."—Seahawks head coach Pete Carroll, commenting on a slimmer-looking offensive lineman James Carpenter, who has changed his diet.
(not tendered offers)
DE Patrick Chukwurah (not tendered as UFA).
LB Leroy Hill (not tendered as UFA).
K Ryan Longwell (not tendered as UFA).
G Frank Omiyale (not tendered as UFA).
RB Christine Michael (2/62): 4 yrs, terms unknown.
DT Jordan Hill (3/87): 4 yrs, terms unknown.
WR Chris Harper (4/123): 4 yrs, terms unknown.
DT Jesse Williams (5/137): 4 yrs, terms unknown.
CB Tharold Simon (5/138): 4 yrs, terms unknown.
TE Luke Willson (5/158): 4 yrs, terms unknown.
FB Spencer Ware (6/194): 4 yrs, terms unknown.
G Ryan Seymour (7/220): 4 yrs, terms unknown.
LB Ty Powell (7/231): 4 yrs, terms unknown.
G Jared Smith (7/241): 4 yrs, terms unknown.
T Michael Bowie (7/242): 4 yrs, terms unknown.
LS Clint Gresham: RFA tendered at $1.323M with no compensation; $1.323M/1 yr.
K Steven Hauschka: UFA; terms unknown.
S Chris Maragos: RFA tendered at $1.323M with no compensation; $1.323M/1 yr.
DE Clinton McDonald: RFA tendered at 1.323M with seventh-round pick as compensation); $1.323M/1 yr.
DE Cliff Avril: UFA Lions; $13M/2 yrs, $11M guaranteed.
DE Michael Bennett: UFA Buccaneers; $4.8M/1 yr.
CB/KR Will Blackmon: FA; $715,000/1 yr.
WR Percy Harvin (trade).
QB Tarvaris Jackson: FA Bills; terms unknown.
DT Tony McDaniel: UFA Dolphins; 1 yr, terms unknown.
QB Brady Quinn: UFA Chiefs; terms unknown.
WR Brett Swain: FA; 2 yrs, terms unknown.
CB Antoine Winfield: FA Vikings; $1.5M/1 yr, $500,000 SB/$1M guaranteed.
DT Alan Branch: UFA Bills; $3M/1 yr.
WR Deon Butler: Not tendered as RFA/Chargers; 1 yr, terms unknown.
DE Dexter Davis (released/failed physical).
QB Matt Flynn (traded Raiders).
DE Jason Jones: UFA Lions; $9.5M/3 yrs, $2.5M SB.
TE Cameron Morrah: UFA 49ers; terms unknown.
WR Ben Obomanu (released).
CB Marcus Trufant: UFA Jaguars; terms unknown.
RB/KR Leon Washington (released).