Lampard had been in charge for just over 18 months, but leaves following five defeats in the last eight games.
In a club statement, Roman Abramovich said;
” This was a very difficult decision for the Club, not least because I have an excellent personal relationship with Frank and I have the utmost respect for him’.
He is a man of great integrity and has the highest of work ethics. However, under current circumstances we believe it is best to change managers.
On behalf of everyone at the Club, the Board and personally, I would like to thank Frank for his work as Head Coach and wish him every success in the future. He is an important icon of this great club and his status here remains undiminished. He will always be warmly welcomed back at Stamford Bridge.”
He will be replaced by Tuchel, following a verbal agreement that has been in place between Chelsea and their incoming manager for a couple of days before the news of Lampard’s departure became public.
It comes just 24 hours after Lampard led Chelsea to a 3-1 win over Luton Town in the FA Cup, but the club’s Premier League form has led to growing concerns.
The 42-year-old achieved a top-four finish last season, which was deemed impressive having taken over when the club were under a transfer ban.
However, this season Chelsea spent £220 million ($275m) on new signings to try and close the gap on Liverpool and Manchester City.
It hasn’t worked, with Timo Werner and Kai Havertz suffering prolonged periods of poor form under their new manager while Chelsea’s performances as a team were increasingly getting worse.
Club chairman Bruce Buck watched on with technical and performance advisor Petr Cech as Leicester City ran out comfortable 2-0 winners against Lampard’s side in their most recent league fixture.
The loss to Brendan Rodgers’ men was just the latest of a series of defeats against the Premier League’s best teams, which recently included reverses against Manchester City and Arsenal.
Chelsea have only beaten West Ham of the top 11 clubs this season, while picking up the second-lowest number of points at this stage of a season since Roman Abramovich bought the club in 2003.