The deal is similar to the 2009 contract that paid Griffey a base salary of $2 million and earned him $3.15 million total with incentives.
"The framework of this year's contract is similar to last year's," Griffey's agent, Brian Goldberg, said by telephone from Cincinnati.
"We're tickled pink that he's decided to come back,'' Seattle general manager Jack Zduriencik said from the GMs meetings in Chicago. "He was such a positive role model, if you will, for a lot of players. He likes where we're headed and he likes what's going on here. He's a first-ballot Hall of Famer and the greatest player in Seattle Mariners history.''
Griffey batted .214 in 117 games with the Mariners last season. But he hit 19 homers, drove in 57 runs and drew a team-leading 63 walks. He was limited by a swollen left knee that required a second operation last month.
After spending his first 11 seasons with Seattle, he played nine more with the Cincinnati Reds and Chicago White Sox. Griffey returned to the Mariners in 2009 under rookie manager Don Wakamatsu and almost single-handedly transformed what had been a fractured, bickering clubhouse with his leadership, energy and constant pranks.
The Mariners finished third in the AL West with an 85-77 record, after finishing last in the division with 61 victories in 2008.
"He went beyond anything that I would have expected," Zduriencik said.
Griffey even turned formerly reclusive star Ichiro Suzuki into a smiling, joking teammate. He had neckties made for road trips bearing Wakamatsu's likeness. He also had the Mariners wearing ties bearing his own likeness and the words "World's Greatest Teammate" for one midseason flight out of Seattle.
"His influence, the presence he has -- there are players on this ballclub who are very excited to know they are going to be teammates again with Ken Griffey Jr.," Zduriencik said.
The Mariners even carried Griffey off the field on their shoulders immediately following October's season finale.
Griffey, who turns 40 on Nov. 21, ranks fifth on Major League Baseball's career list with 630 home runs.
"I'd like to thank the Mariners organization for inviting me back to play in 2010," Griffey said in a statement. "While 2009 was an awesome experience for me, my ultimate goal is for the Mariners to get to and win the World Series. To that end, I look forward to contributing in any role that Don sees fit on the field, and any manner I possibly can off the field."
Seattle is convinced Griffey is healthy enough to contribute again next year -- though he won't undergo a physical to formally close his new deal for a couple more weeks, to give his knee time to recover from the surgery.
"We feel real good about information we've gotten from Dr. [Timothy] Kremchek," Zduriencik said of the Cincinnati-based surgeon who removed a bone spur in Griffey's knee on Oct. 26.
Jerry Crasnick covers baseball for ESPN.com. Information from The Associated Press was used in this report.