The Senegal international is expected to complete a move to Saudi Pro League side Al-Diriyah on an initial one-year contract.
With his exit now finalised, David Moyes is expected to move for a replacement in central midfield, and Parma's Mandela Keita has been strongly linked as a target in the opening weeks of the transfer window.
The 24-year-old Belgian international, who joined Parma from Royal Antwerp in 2024, made 40 appearances across all competitions last season and has already been the subject of contact between the two clubs, according to Sky Sport Italia.
Everton are not alone in their interest. Aston Villa and Leeds United have also been credited with tracking Keita, and both clubs are said to be capable of meeting Parma's valuation of the player should they decide to move for him.
For now, Everton's need is arguably the most pressing, with Gueye's exit leaving a gap in Moyes's central midfield options following a season in which the veteran remained a regular starter despite his advancing years.
Everton have already made one addition to the middle of the park this summer in Hayden Hackney from Middlesbrough, but Gueye's departure means a further reinforcement is likely to be required before the new season begins.
Villarreal's Pape Gueye has also been mentioned as an alternative option for Everton, though Keita remains the name most consistently linked with Goodison Park in recent weeks. Parma, for their part, are expected to hold out for a fee that reflects Keita's importance to their own midfield unless one of his suitors meets their asking price.
Gueye leaves as one of the most popular figures of Everton's recent history, having first joined the club in 2016 before a spell at Paris Saint-Germain and a return to Merseyside in 2022. Everton confirmed his exit on social media with a farewell message thanking him for his service.
Moyes now faces the task of reshaping his engine room without one of its most consistent performers of the past decade.