Tuchel has penned an 18-month contract with the Blues with the option of an extension.
“I would like to thank Chelsea for their confidence in me and my staff,” he said. “We all have the greatest respect for Frank Lampard’s work and the legacy he created at Chelsea.
“At the same time, I cannot wait to meet my new team and compete in the most exciting league in football. I am grateful to now be part of the Chelsea family – it feels amazing!”
The Blues sit 10th in the Premier League after just one win in their last five games but director Marina Granovskaia is confident the change in leadership can spark a turnaround in fortunes.
“It is never easy to change head coach in the middle of the season but we are very happy to secure one of Europe’s best coaches in Thomas Tuchel,” she added.
“There is still much to play for and much to achieve, this season and beyond. We welcome Thomas to the club.”
Tuchel will take training on Tuesday evening with Wolves in the Premier League his first match in charge on Wednesday.