It is reported that the 28-year-old pulled out of a training session to complete talks and is now headed for Stamford Bridge, London.
Chelsea had reportedly reached an agreement with the shot-stopper over a five-year contract but with Rennes demanding a higher fee for their man, a move had stalled.
The first offer of around €20 million (£18m/$24m) was rejected, however, it is reported that both clubs have finally agreed on a fee around €28m (£25m/$33m).
On Friday morning, Mendy was spotted leaving a training session with his agent, before attending a meeting with club president Nicolas Holveck to conclude discussions.
Former Chelsea goalkeeper and club legend Petr Cech, who is the club’s technical and performance advisor, and Christophe Lollichon, were reported to have identified Mendy as a top target for the Blues after they all arrived Chelsea from Rennes themselves.
Rennes Head coach Julien Stephan spoke about a selection issue ahead of this weekend’s action against Nimes, as the Ligue 1 outfit are on the lookout for a replacement for Mendy.
He said: “Edouard has an exceptional opportunity, humanly, we have to hear it,” Stephan said to the French media.
“But we must allow time for negotiations. [A substitute?] Obviously, we are looking.”
Mendy played a key role for Rennes, featuring in 34 games, as they historically secured an unprecedented qualification to the UEFA Champions League.
At 6 feet 6 inches, Mendy would come into the squad to challenge Kepa, who struggled last season in both shot-stopping and set-pieces.
Chelsea are now on course to a summer spending spree of over £230 million, after already securing the services of Hakim Ziyech from Ajax, Timo Werner from RB Leipzig, Leicester City’s Ben Chilwell and Kai Havertz in a record £71 million deal from Bayer Leverkusen.