Posey, 34, has played his entire 12-year career in San Francisco, helping the team win three World Series titles, in 2010, 2012 and 2014. He is the only player still on the Giants who played on all three title-winning teams.
The Giants said last month that they would exercise Posey's $22 million club option for the 2022 season as long as the veteran catcher wanted to keep playing after a stellar year.
Posey hinted during the playoffs he might be done, saying he was ready to embrace more family time with four young children at home.
"I'm definitely just going to take some time with my wife, talk with her, be able to be a full-time dad of four kids for the first time in a while,'' Posey said. "Yeah, just kind of take it slow and see how things progress.''
Posey opted out of the coronavirus-shortened 2020 campaign to help care for prematurely born adopted twin girls. He and his wife, Kristen, also have twins Lee and Addison, who just turned 10.
Posey, whose contract includes a $3 million buyout, helped lead the Giants to a franchise-record 107 wins and their first National League West title since 2012 by playing regularly down the stretch as he demonstrated his health and durability.
He batted .304 with 18 homers and 56 RBIs, showing his surgically repaired right hip had finally regained full strength three years after the operation. Posey would be one of six players in the divisional era to hit .300 or better in his final MLB season, according to ESPN Stats & Information research.
The 2010 NL Rookie of the Year, Posey came back from a devastating season-ending leg injury in 2011 to win NL MVP the following year.
He tore three ligaments in his left ankle and broke a bone in the lower leg when he was run over by the Marlins' Scott Cousins on May 25, 2011. Posey responded by winning the 2012 batting crown and MVP honors while leading the Giants to a second World Series championship in a three-year span.
Posey advocated for rules to better protect against home-plate collisions to avoid injuries for both catchers and baserunners alike.
"I try to keep myself out of the conversation as much as I can because I know people are going to connect me to it regardless,'' Posey said in January 2014. "I'm just kind of sitting back and letting the higher powers hammer it out. I have my thoughts but I'll keep them to myself."
Posey was selected by the Giants fifth overall in the first round of the 2008 draft out of Florida State, where in May 2008 he played all nine fielding positions in the same game.
"Buster Posey hangs 'em up. What an incredible career for a lifelong Giant,'' former Oakland Athletics left-hander Dallas Braden wrote on Twitter. "The statue is already being built.''
Posey is a lifetime .302 hitter, making him one of six catchers in major league history to start 1,000 games at catcher and have a lifetime batting average of .300 or greater (pending inclusion of Negro League statistics).
The Associated Press contributed to this report.