Genesio was appointed Les Rouges et Noir manager in March 2021 following the initial departure of Stephan, having previously taken charge of Beijing Guoan and Lyon.
In his first full season in charge, Genesio led Rennes to the last 16 of the Europa Conference League, where they were eliminated by Leicester City, and guiding Les Rouges et Noir to a fourth-placed finish in Ligue 1.
Rennes' ranking earned them a route into the Europa League group stages, although their continental run ended at the hands of Shakhtar Donetsk in the knockout round playoffs, and Genesio's side once again missed out on a spot in the Champions League with another fourth-placed finish in the top flight.
Les Rouges et Noir went through their first eight games of the 2023-24 season undefeated, but five of those contests ended in draws, and Genesio's side have left a lot to be desired heading into the winter months.
While Rennes have won three of their opening four Europa League group-stage matches this season, they have endured a miserable domestic run with four losses and a draw from their last five Ligue 1 contests.
Les Rouges et Noir entered the November international break on the back of successive defeats to Nice and Lyon, the latter of whom had not won a single Ligue 1 game this season before a 1-0 triumph at Roazhon Park, which left Rennes 13th in the top-flight table.
Following Rennes' troubled start to the season, Genesio has now stood down from his position due to a combination of sporting and personal reasons, and Stephan has made a surprise return to Roazhon Park to succeed the 57-year-old.
"Bruno Genesio is leaving his position as general coach of Stade Rennais F.C., he will be replaced by Julien Stephan," Les Rouges et Noir said in a statement on Sunday afternoon.
"By mutual agreement with Stade Rennais F.C., and for personal reasons in particular, Bruno Genesio is leaving his position as general coach.
"Arriving at the club on March 4, 2021, Bruno Genesio qualified the SRFC each season for a European competition and was elected best coach in Ligue 1 in 2022. Stade Rennais F.C. salutes his career in Rouge et Noir, thanks him for the work accomplished and wishes him the best for the rest of his career.
"The club management will hold a press conference on Monday November 20, 2023 at 2 p.m. On this occasion, Julien Stephan, appointed head of the first team, will be presented to the press."
Before making way for Genesio, Stephan managed 110 games for Rennes between 2018 and 2021, winning the Coupe de France in 2019 and leading Les Rouges et Noir to the Champions League group stage for the first time ever.
Stephan resigned midway through the 2020-21 season following a run of four straight defeats, and the 43-year-old spent one-and-a-half seasons in charge of Strasbourg until January 2023, when he was sacked after an eight-game winless streak.