The club's board acted swiftly to dismiss Martinez in the wake of his side's 3-0 defeat at Sunderland, which kept the Wearside outfit up and extended Everton's recent run to one win in their last 10 games.
The 42-year-old was to have faced protests from fans at the club's player of the year dinner, scheduled for Thursday but which has now been postponed, and at this weekend's final home game against Norwich City.
But now attention will turn to appointing a successor to the Spaniard with Frank de Boer - who resigned from his role as Ajax coach on Thursday - emerging as the clear early favourite.
Martinez, who succeeded David Moyes in 2013 and had three years left on his contract, had insisted at the Stadium of Light that the players were still 100 per cent behind him.
But the board, including new majority shareholder Farhad Moshiri, clearly disagreed, issuing a statement which read: "Everton Football Club regrets to announce that Roberto Martinez has left his position as first team manager with immediate effect.
"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.
"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."
Martinez joined Everton in 2013 after leading Wigan Athletic to an unlikely FA Cup triumph, and took them to fifth place in his first season in charge.
But a testing current campaign slumped to a new low in a 4-0 derby defeat to Liverpool last month, and an FA Cup semi-final defeat to Manchester United all but ended any hopes Martinez had of retaining his role beyond the northern summer.
The timing of Martinez's departure will inevitably fuel speculation over a move for De Boer, who leaves Ajax having failed to win back the Eredivisie title from arch-rivals PSV Eindhoven last weekend.
De Boer's agent has previously indicated his client would be interested in the Goodison Park job, and his brother Ronald told Sky Sports on Thursday: "In my eyes he's the right man for the job but it's up to Everton to make their move."
Outgoing Manchester City boss Manuel Pellegrini and former boss Moyes are also seen to be among the contenders.
In the meantime, the club announced David Unsworth and Joe Royle will be in charge for this weekend's final game of the season against Norwich.