Lampard was hired by Everton to replace Rafael Benitez in January 2022, but the former Chelsea boss leaves with the team languishing 19th in the table.
Everton fell to a damaging 2-0 defeat at relegation rivals West Ham on Saturday -- a ninth loss in their past 12 Premier League matches which left them level on points with bottom club Southampton.
Everton owner Farhad Moshiri had previously offered public backing for Lampard.
But the tame surrender at West Ham proved the final straw for Moshiri, who was at the game to watch Everton for the first time in 14 months.
After several hours of reports that Lampard had been sacked, Everton finally confirmed the 44-year-old's departure on Monday evening.
"Everton Football Club can confirm that Frank Lampard has left his post as senior men's first team manager today," a club statement said.
"Everyone at Everton would like to thank Frank and his coaching staff for their service during what has been a challenging 12 months.
"Frank and his team's commitment and dedication have been exemplary throughout their time at the club, but recent results and the current league position meant this difficult decision had to be taken.
"We wish Frank and all his backroom team well for their future in the game.
"The club has started the process to secure a new manager and will provide updates on the appointment in due course."
Paul Tait and Leighton Baines will take training until a new manager is appointed, with Everton's next game against Premier League leaders Arsenal on February 4.
Everton felt compelled to act over Lampard's future as they fight to avoid playing outside the top flight for the first time since 1954.
Lampard arrived at Everton 12 months ago with the team languishing in 16th place and the former Chelsea and England midfielder initially looked a shrewd appointment, helping the Merseyside club avoid relegation.
Fuelled by fervent backing from their fans at Goodison Park, the Toffees beat the drop by winning three of their last six league matches, including a dramatic 3-2 success against Crystal Palace that preserved their top-tier status.
But Everton are now looking for their eighth permanent manager in less than seven years after Lampard failed to build on the momentum from that successful end to last term.
In a sign of the turmoil enveloping Everton, club directors were earlier this month ordered to stay away from Goodison Park due to perceived security risks.
Lampard won only 12 of his 44 matches in charge of Everton in all competitions.
Former Burnley boss Sean Dyche, ex-Leeds coach Marcelo Bielsa and West Ham's former Everton manager David Moyes are among the potential candidates to replace Lampard, according to bookmakers.
Al-Ittihad boss Nuno Espirito Santo, formerly of Wolves, and ex-Everton striker Wayne Rooney, now in charge of MLS side DC United, have also been mooted as possible contenders.
Hampered by the sale of Brazil forward Richarlison to Tottenham in the close season, Everton managed only three wins in 20 league games this term against a backdrop of mounting fan fury.
There have been widespread protests against the board and Lampard at recent games.
Supporters staged a sit-in demonstration after the recent loss to Southampton, with Everton defender Yerry Mina and team-mate Anthony Gordon confronted by fans when they left Goodison Park in their cars.
Responding to Lampard's sacking, Everton fans' group 'NSNOW' called for Moshiri to "stop the rot".
"Nothing tells the story of Everton's mismanagement under the current owner and board more than the fact we now need to appoint our eighth 'permanent' manager since 2016," the statement said.
"The chaos and dysfunction within Everton's leadership has got us into this position. The owner needs to take urgent and radical steps to stop the rot. Or sell to someone who will."
For an optimal experience, please
