The 52-year-old Portuguese had been in his second spell at the club, taking charge in June 2013.
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.
“All at Chelsea thank Jose for his immense contribution since he returned as manager in the summer of 2013.
Mourinho: ‘The Unhappy One’
“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.
“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.”