Daryl McMahon has left his position as Ebbsfleet United manager "by mutual consent", ending a three-and-a-half-year spell in charge.
McMahon, 36, won promotion to the National League during his time in charge and led the club to the play-off semi-finals last season.
The Fleet are 15th in the division, with six wins from 19 games.
"This is a disappointing day for myself and the board," chairman and owner Dr Abdulla Al Humaidi said.
"Daryl has worked tremendously hard in getting this club into the National League and consolidating us there."
Former West Ham midfielder McMahon, who also spent two years at Ebbsfleet as a player, also lists Leyton Orient and Stevenage among his former clubs.