Evans served as San Francisco's general manager for four seasons prior to being removed. He's been a part of the organization for 25 years.
"I want to thank Bobby for his tireless work on behalf of the Giants," team president Laurence M. Baer said in a statement. "He played an important role in our team's success throughout his tenure, which includes three World Series championships, four NL pennants and eight playoff appearances."
The Giants intend to reassign Evans within the organization. Schulman reported that manager Bruce Bochy and team executive vice president Brian Sabean are expected to retain their jobs. In a statement, Sabean said that he looks forward to "working closely" with Baer as the club launches its search for Evans's replacement.
The Giants entered Monday in fourth place of the National League West division with a record of 72-84.
San Francisco clinched its second straight losing season earlier this month. Last year, the club went 64-98, which was tied with the Tigers for the worst mark in baseball.