The three-time Pro Bowl selection and 2005 NFL Defensive Rookie of the Year said on his website Tuesday night that he intends to file retirement papers.
"I retire today not because I don't feel I can go out there and still play the game at a very high level," Merriman wrote. "I am retiring because I want to retire on my own terms and leave while I know I can still physically play the game."
The team later confirmed Merriman's intentions in a text message and on its Twitter account.
The 28-year-old Merriman also posted a note on his Twitter account, which included a link to his website (shawnemerriman.com). "I have a very Big announcement," Merriman wrote. "Thanks everybody."
The decision comes a week before he was eligible to become a free agent, and after spending parts of the past three seasons in Buffalo. That included last year, when he was cut by the Bills in August only to be re-signed by Buffalo in October to help address the team's injury-riddled defense.
Merriman had expressed surprise he went unsigned for the first six weeks of last season. He returned to the Bills with a noticeably sun-burnt face, sheepishly explaining he had fallen asleep on the beach after working out at his home in Miami.
In signing a one-year $700,000 contract, Merriman finished last season with 17 tackles and one sack in 10 games, including one start. That was a marked drop-off for a player who became an instant NFL star after being selected by San Diego 12th overall in the 2005 draft.
Combining for 39 1/2 sacks in his first three seasons with the Chargers, Merriman earned the nickname "Lights Out" as one of the league's fiercest pass rushers.
A series of injuries, however, caught up to him, and he was particularly bothered by a sore right Achilles tendon. It's an injury that led to the Chargers waiving him during the 2010 season.
The Bills acquired his rights soon after, but Merriman never made it past his first practice in Buffalo after aggravating the injury. He was limited to playing five games in 2011 before being placed on injured reserve to have surgery to repair the partially torn tendon.
Each offseason in Buffalo, Merriman declared himself to be fully healthy, and ready to regain his dominant form.
Last spring, Merriman compared himself to Benjamin Button, the fictional movie character who aged in reverse.
"I feel young," he said. "Anybody that will get a chance to watch me this year will see I'm moving around as I did when I came into the league."
By the end, his play never matched his bold pronouncements.
Merriman was limited to 18 games over his final three seasons. And he finished with 45 1/2 career sacks in 75 games, including 59 starts.
Merriman also made headlines for his on- and off-field troubles.
In 2006, he was suspended by the NFL for four games after testing positive for steroids. He blamed the positive test on a tainted supplement, which he never identified. Despite being limited to playing 12 games, Merriman finished with a career-best 17 sacks that season.
In 2009, Merriman was arrested just before the season after reality television star Tila Tequila accused him of battery and false imprisonment at his suburban San Diego home. No charges were filed, and Merriman and Tequila settled dueling lawsuits.
Though it was unlikely the Bills were going to re-sign him, Merriman's retirement marks the latest change to the team's defense under new coach Doug Marrone, and new coordinator Mike Pettine.
The Bills this offseason have already released three veteran defensive players: cornerback Terrence McGee, safety George Wilson and linebacker Nick Barnett. Last week, defensive lineman Chris Kelsay announced his retirement after 10 seasons in Buffalo.
In thanking his fans and two former teams, Merriman said he intends to pursue other career opportunities. Merriman has dabbled in acting, is a fan of kick boxing and wrestling and has also worked as a model.
In January, Merriman showed off his tattoos as a model for PETA's "Ink, Not Mink" campaign, to encourage people not to wear natural fur coats.
"I feel truly blessed to have been part of the NFL, and to have had the opportunity of a lifetime," Merriman wrote. "I will continue to train with some of the guys not because of football, but it's part of my Lifestyle."