In a statement on his Web site, Valentine, who led the Marines to the Japan Series championship in 2005, said leaving the club "is best for the Chiba Lotte Marines."
Lotte management had decided before the season that it could not afford Valentine and would not renew his contract, which brought protests from fans, who staged nightly vigils at Chiba Marine Stadium and submitted a petition with more than 100,000 signatures to the team's front office, according to The Associated Press.
The Marines (34-48) are currently 15 games out of first place in the Pacific League.
Valentine, 59, began his first stint with the Marines in 1995. In the Major Leagues, he served the better part of eight years as skipper of the Rangers (1985-92) and seven with the Mets (1996-2002), compiling a record of 1,117-1,072. The Mets won the National League pennant in 2000.
Alden Gonzalez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.