Peter Trego will leave Somerset at the end of the season, after the club decided not to renew his contract.
Trego signed a white-ball-only deal for the 2019 season, after losing his regular place in the Championship side. He scored 389 runs at 35.36 in the club's victorious Royal London Cup campaign, but was dropped from the T20 side after struggling against Rashid Khan in a defeat against Sussex.
Trego, 38, has not retired from the game, and a club statement said he would "consider other opportunities".
He leaves Somerset having scored over 18,000 runs for the club in all formats and having taken more than 500 wickets since his debut in 2000.
Trego originally broke into the side as a bowling allrounder, and had spells at Kent and Middlesex before re-joining Somerset in 2006. It briefly looked as though he would give up the game for a career in football, after he spent the 2004-05 season playing in goal for Margate.
A prolific run-scorer in one-day cricket, he was perhaps unfortunate never to get a run in England's limited-overs sides, having played for the Lions in 2010 before scoring over 1,000 white-ball runs across List A and T20 cricket in 2013.
He took 50 Championship wickets once, in the 2012 season, but as his career progressed he began to bowl less and take his red-ball batting more seriously, making 1047 Championship runs in 2016.
He was a regular in the early days of the T20 franchise circuit, spending winters in Zimbabwe, Bangladesh and New Zealand, and scored a match-winning 70 in Somerset's win against Kolkata Knight Riders in 2011 which took them through to the group stage of the Champions League T20.
He lifted a trophy for the club for the first time in May, having previously played in five final defeats, making 29 as Somerset beat Hampshire in the Royal London Cup.
Andy Hurry, Somerset's director of cricket, said that Trego would be "remembered as one of Somerset cricket's great characters".
"This year we have seen the emergence of several young players and this has meant that Pete's opportunities in the first XI have been limited," Hurry said. "He obviously wants to be playing first-team cricket, which is not something that we can guarantee him here at the moment, and therefore we feel that it is in both the club's and Pete's best interests for him to consider other opportunities."
Trego said: "I understand the Club's desire to give younger players an opportunity, and whilst I'm no longer going to be a Somerset player, I will always be a Somerset fan.
"It's been a long and fantastic journey. I've got so many wonderful memories, but that final one-day game at Lord's has to stand out. Walking around the ground with the trophy and long-standing teammates such as Hildy [James Hildreth] was the icing on the cake of what's been a great time in my life."