The former goalkeeper hung up the gloves after two seasons away with Arsenal.
And last week, Cech was named Chelsea's new technical and performance advisor.
He told the club's website: "I wanted to consider every possible option I had and I have to say I had so many options to keep playing because everybody was trying to persuade me to carry on playing.
"So I had this on the side and I had offers from various places to continue in different roles but this offer I got from Chelsea is personal to me because I had a great history with this football club.
"It was the best offer for me to consider and in the end I feel really happy and privileged to have this opportunity to come back and especially in the role I have, which is a role with a lot of responsibility and this is something I am really looking forward to."
Cech added: "I have to say I know this club at Chelsea very well. I know the majority of people who are still at the club, I have worked with them, and so I am not stepping into something that is completely unknown to me. I have a very good idea how the club is run and the club has had amazing success over the past 15 years and we would like to carry on with that and continue with the same success, and even better success in the forthcoming years."