The Blues confirmed the goalkeeper’s arrival from Rennes earlier today and he could be involved against West Brom this weekend.
The Senegal shot-stopper arrived from the Ligue 1 side in a £20m deal earlier today.
Meanwhile, the Senegalese international has penned a five-year deal at Stamford Bridge and will compete with Kepa Arrizabalaga for a starting spot between the posts in the season ahead.
Mendy said: “I am so excited to be joining Chelsea.
“It’s a dream for me to be a part of this exciting squad and to work with Frank Lampard and all of his coaching staff.
“I look forward to meeting my team-mates and can’t wait to get started.”
“I’ve been a Chelsea supporter since I was little. I adore this club,” Mendy told the Chelsea website.
“When I was 12 I had the chance with a past club I played for to go to Brighton, and we watched a match. I thought English football was amazing.
“We went into a shop and I saw the Chelsea shirt, this was about 2003 when Ranieri was the manager, and I bought this shirt. So I’ve always liked this club.”