"It's been an incredible 27 years and I've loved every minute of it. However, everything has to come to an end eventually. I've been discussing my future with the club and my family for a while and we felt that now was the appropriate time to make this announcement in order for both the club and me to put plans in place," Trescothick said in an official statement released by county Somerset.
"There's still a lot of the season left, and I'll be doing everything I can to put in performances for the Second XI in order to force my way back into contention for the first team. This club, the members and the supporters mean so much to me. There are so many memories that I will cherish forever, and the club will always hold a truly special place in my heart," he added.
Trescothick made his debut for Somerset in 1993 and also holds a record for the most first-class catches (445) for the county. The English county great went on to play 76 Test matches for the team. The batsman scored more than 5800 runs for the side at an average of 43.79.
He scored 4335 runs in the ODI format at an average of 37.37. He also captained England, and he even went on to win an Ashes series in 2005.
"Marcus Trescothick is one of the finest players that this country has ever produced, and his record on the field of play speaks for itself. His passion and enthusiasm for the game of cricket is infectious, and his work ethic is phenomenal. He is the absolute personification of what a professional sportsman should aspire to be," Somerset Director of Cricket, Andy Hurry said in an official statement.
"Whilst his playing record is there for all to see, what you can't measure is the positive influence that he has behind the scenes. He leads by example in everything that he does, and the way that he goes about his business is second to none," he added.