The 52-year-old Portuguese had been in his second spell at the club,taking charge in June 2013.
Chelsea finished eight points clear last season and won the League Cup, but have lost nine of their 16 league games so far and are 16th in the table, one point above the relegation places.
Mourinho’s final match was Monday’s 2-1 defeat at leaders Leicester City.
Pep Guardiola, Guus Hiddink, Brendan Rodgers and Juande Ramos have all been touted as possible successors as Blues owner Roman Abramovich begins another managerial search.
“Chelsea Football Club and Jose Mourinho have today parted company by mutual consent.
“All at Chelsea thank Jose for his immense contribution since he returned as manager in the summer of 2013.
“His three league titles, FA Cup, Community Shield and three League Cup wins over two spells make him the most successful manager in our 110-year history.
“But both Jose and the board agreed results have not been good enough this season and believe it is in the best interests of both parties to go our separate ways.
“The club wishes to make clear Jose leaves us on good terms and will always remain a much-loved, respected and significant figure at Chelsea.
“His legacy at Stamford Bridge and in England has long been guaranteed and he will always be warmly welcomed back to Stamford Bridge.
“The club’s focus is now on ensuring our talented squad reaches its potential.
“There will be no further comment until a new appointment is made.”