The 43-year-old had played 76 Tests for England. He piled up 5,825 Test runs at an average of 43.79 in an international career that spanned from 2000 to 2006.
Trescothick made his Somerset debut in 1993 and scored 19,654 first-class runs for the county.
"I'm extremely grateful for all the support that I've received throughout this remarkable journey," he was quoted as saying by BBC.
"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 I to put plans in place," he added.