Nice are on a run of five consecutive defeats in all competitions and Thursday’s 3-2 defeat to Bayer Leverkusen in the Europa League was preceded by fans’ protests demanding Vieira’s removal.
Vieira joined Nice from Major League Soccer side New York City in the summer of 2018.
The former Arsenal captain led Nice to a seventh place finish in his debut season and a fifth place finish last season saw them earn a spot in this season’s Europa League group stage.
Nice are currently third in their Europa League group and 11th on the Ligue 1 table.
Assistant manager Adrien Ursea has been tasked with leading the team from now on.
A club statement, confirming the decision to part ways on Friday, said: "Patrick Vieira, who joined the club in the summer of 2018, is no longer head coach of OGC Nice, effective immediately.
"In a meeting conducted after last night's match, the Nice Board informed Patrick Vieira of their decision to end their collaboration.
"The Rouge et Noir club has decided to appoint Adrien Ursea as head coach of the club's professional first team, as of today.
"The Swiss-Romanian tactician, who was assistant coach to Patrick Vieira and, before that, Lucien Favre, will take charge of his first Nice match as head coach this Sunday with the trip to Reims.
"Patrick Vieira put all his heart and professionalism into his service for OGC Nice over the last two and a half years of their collaboration.
"The Nice board sincerely thanks the former France international for his commitment and dedication to the development of the club and wishes him every future success in his coaching career."
