Strachan, who had planned to quit the club at the end of the season, has stepped down with immediate effect after two-and-a-half years in charge.
"Gordon and I met yesterday and have both concluded that it is in the best interests of the club that he steps down with immediate effect," chairman Rupert Lowe said.
Steve Wigley will be in charge of first team affairs until the end of the season or until a new boss is appointed.