The Belgian said his contract was running out in August but he would be leaving immediately.
Gambia was his 10th job as a national team coach and by far his most successful. He qualified the small west African country for their first Cup of Nations in Cameroon two years ago and then took them on a giant-killing run to the quarter-finals.
They qualified again for the tournament in the Ivory Coast but lost all three Group C matches, although they were leading Cameroon 2-1 at the Stade de la Paix with five minutes to play on Tuesday in their last group game before going down 3-2 to finish bottom without any points.
His first national team job was with Namibia in 2008, and he was then coach of Zimbabwe, Ethiopia, Yemen, Malawi, Togo, Bangladesh, Trinidad & Tobago and Malta before Gambia.
Saintfiet is the first managerial casualty of this Cup of Nations.
