Still became the youngest manager in Europe's top five leagues at age 30 when he took over at Reims last season, with the club paying a fine of 25,000 euros per match until he started his UEFA Pro coaching licence course.
Reims, who went on a 19-match unbeaten streak under Still last season, have lost their last three games including Sunday's 4-1 loss at bottom side Clermont Foot. They are 11th in the table and have not won since March.
"We are proud to have been able to contribute to the emergence of a coach who has been able to impose his convictions and his own style of play," club chairman Jean-Pierre Caillot said in a statement.
Still, who was born in Belgium to English parents, said he would be forever grateful to everyone at Reims.
"I will always be the number one supporter of the Rouge et Blanc," he added.
Reims, who have 40 points from 31 matches, visit third-placed Brest on May 10th.
