The newcomer has scored just one point so far this season, with McLaren struggling to get strong performances from their Honda engine.
"I'm delighted that the team has now formally announced that I will continue to race for them next year, because I'll be able to approach the second half of my rookie season with total focus on the job in hand," he said in a statement.
McLaren Racing Director Eric Boullier said the plan had always been for Vandoorne to continue as part of a multi-year deal.
"That plan hasn't changed, and I'm very happy therefore to be able to confirm that he'll continue to race for us next season," said the Frenchman.
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"Like all rookies, he's had to learn a lot in the first half of his first Formula One season, but we have great confidence in him, and he's getting better and better all the time."
McLaren's other driver, Spain's double world champion Fernando Alonso, has yet to decide his future and wants to be assured of a competitive car before committing to McLaren.
(Reporting by Alan Baldwin; Editing by Keith Weir)
