The Merseyside club confirmed the Dutchman's departure on Monday afternoon.
"Everton Football Club can confirm that Ronald Koeman has left the Club," read a statement.
"Chairman Bill Kenwright, the Board of Directors and Major Shareholder Farhad Moshiri would all like to express their gratitude to Ronald for the service he has given to the Club over the past 16 months and for guiding the Club to seventh place in last season’s Premier League campaign."