On Tuesday, the 22-year-old completed a three-year deal from Swiss top-flight side Grasshopper.
After struggling for game time in Italy with Serie B sides Bari and Vicenza, the left-back found his feet in the Swiss Super League. He also earned an invitation to Cote d'Ivoire national team last year.
His recent form attracted interests from Porto and some German clubs but former PSG youth player opted for the Reds and Black.
The move reunites Doumbia with his former PSG teammate James Lea Siliki and brings him closer to his family base in Paris.
"There were several teams, including one that was playing in the Champions League, but Souley wanted to come to Rennes,” Barkat said.
“He loved the speech of the President, Didier Roudet and the coach [Julien Stephan], conquered by the facilities and when he saw the stadium, he told me 'Ghouti, what's this crazy thing?'
Meanwhile, club chairman Olivier Létang is relishing the qualities the Ivorian midfielder will bring to Julien Stephan’s side as they aim for a place in Europe.
"We are delighted to welcome Souleyman Doumbia who is a boy who was asked by many clubs in Europe," Letang told club website.
“Souleyman arrives with great humility to join our squad and participate in the Stade Rennais FC project,” Letang told club website.
Doumbia could make his Ligue 1 debut against Montpellier at the Roazhon Park on Sunday.