Considered one of the greatest players to have ever played at Stamford Bridge, Lampard left the Blues in 2014 having won three English Premier League titles during 13 years at the club.
“Everyone knows my love for this club and the history we have shared. However, my sole focus is on the job in hand and preparing for the season ahead.
“I am here to work hard, bring further success to the club and I cannot wait to get started.”
‘One of the most talented young coaches’
The former England international spent last year as manager of Derby County, which plays in the second tier of English football.
“It gives us great pleasure to welcome Frank back to Chelsea as head coach,” said Chelsea director Marina Granovskaia.
“Frank possesses fantastic knowledge and understanding of the club and last season, he demonstrated he is one of the most talented young coaches in the game.”
Chelsea launched an appeal to Switzerland’s Court of Arbitration for Sport over the transfer ban.
To make matters worse, the Blues also lost star player Eden Hazard to Real Madrid earlier in the window.