Daniel Abt will move from ART to Hilmer for the 2014 GP2 season.
The 20-year-old German was only narrowly beaten to the 2012 GP3 title by Mitch Evans, and stayed with ART to graduate to GP2 this year.
But he had a luckless debut season in the Formula 1 feeder category and took only one top-five finish on the way to 22nd in the standings.
Abt signed for Hilmer after testing with the team in the post-season Abu Dhabi sessions earlier this month.
"First of all, I'd like to thank ART," said Abt.
"The team gave me the opportunity to gather a lot of important experience in the GP2 series.
"But now the time has come to take the next step and I'm very happy that the cooperation with Hilmer has worked out."
Franz Hilmer's team replaced Ocean in the GP2 field this year and won races with Robin Frijns and Jon Lancaster.
"In Daniel we've gained a driver who absolutely corresponds to our wishes," said Hilmer.
"In the coming season we're going to show how powerful this Bavarian-Bavarian combination is.
"In the tests he gave an indication of his true abilities in our car."