Earls, who does not have a job to go to, has recently been on extended sabbatical from the agency.
During his time in the role he was responsible for restructuring O&M's planning operation, consolidating its disparate teams into one large department.
The agency is already seeking a planner to head its UK department, but has not decided whether or not it will replace Earls in the Europe role.
He joined O&M in 2001 after spending two years as the planning director at St Luke's. It is not yet known who will replace him.
Daniel Sicouri, O&M's chief executive for the Europe, Middle East and Africa region, said: "Mark contributed a great deal to the establishment of Ogilvy's strong reputation for planning in London and across Europe.
Earls added: "I have really enjoyed my time helping to rebuild the reputation O&M has for planning.
"I wish Ogilvy internationally all the best for the next stage of the journey."
Before joining St Luke's, Earls was the head of planning at Bates UK.
Before that, he spent five years at Still Price as a board planner. He has also worked at DDB and Grey.
He is currently writing a follow-up to his 2002 book Welcome to the Creative Age.