In place since joining from Wigan Athletic in 2013, the 42-year-old Spaniard paid the price for a run of one win in 10 league games and an FA Cup semi-final defeat at the hands of Manchester United.
"Everton Football Club regrets to announce that Roberto Martinez has left his position as first team manager with immediate effect," the club announced in a statement on their website.
Martinez departs with Everton 12th in the league table ahead of their final game of the season at home to Norwich City on Sunday.
"The chairman and the board of directors would like to place on record their thanks for the dedication and commitment Roberto has shown during his three seasons with the club," Everton added.
"Roberto has been a great ambassador for the club, conducting himself, at all times, with the utmost integrity and dignity.
"He secured the club its highest ever Premier League points total, a place in the last 16 of the Europa League and appearances in both domestic cup semi-finals.
"He has also played a key role in the development of several young players, managing their progression to the Everton first team and international honours."
The club also announced that they have postponed their end-of-season awards ceremony, which had been due to take place in Liverpool on Thursday.
Martinez joined Everton after leading Wigan to FA Cup glory and relegation in the same season, replacing the Manchester United-bound David Moyes, and took the Merseyside club to a fifth-place finish in his first season.
He promised to steer Everton into the Champions League, but they finished 11th last season and have failed to compete for a European place this season, despite reaching the semi-finals of both domestic cups.
Martinez has helped to bring on talented young players such as England internationals John Stones and Ross Barkley and prolific Belgian striker Romelu Lukaku.
But his team's defensive shortcomings have become increasingly apparent in recent months and he has angered supporters by repeatedly emphasising the positives.
A banner saying "TIME TO GO ROBERTO" was flown over Goodison Park during their 2-1 win over Bournemouth last month and fans remained in the ground after the match to protest against him and chairman Bill Kenwright.
Martinez's sacking follows Iranian businessman Farhad Moshiri's arrival in February as the club's new majority shareholder.
Frank de Boer, who left Dutch giants Ajax earlier on Thursday, has been touted as a potential candidate to succeed Martinez.
Original source: Everton confirm sacking of manager Martinez