Alexander Rossi has joined Marussia as the team's official reserve driver.
Rossi has undertaken the role for Caterham for the past couple of years but departed the team following its takeover by a group of Swiss and Middle Eastern investors.
Rossi, 22, will deputise for either Jules Bianchi or Max Chilton in the event that they are unable to compete.
"Today is a good day and next step in my Formula 1 career," said Rossi.
"Since my initial discussions with the Marussia management, I’ve felt right at home. I’m looking forward to working with the team in Hungary and building for the rest of the season. The timing of my affiliation with the team is perfect, especially beginning in Hungary before the summer break.
"My goal is Formula 1, and I’m delighted to be immersed into the team as official reserve driver, where I have the opportunity to prepare for this next step, with plans to drive in Friday practice this season.
"Marussia is in an exciting place right now and the progress at the team is clear for all to see. I’m thrilled that now I have the chance to be part of that journey, to progress and play a useful role in the development of the team. I want to thank Marussia for the opportunity this season."
Team principal John Booth said that Marussia has been impressed by Rossi's progress across the past few years.
"He is a proven talent whom we have observed in GP2 and we have also been impressed by his performances during Friday morning free practice sessions over the past two seasons," he said.
"The US is an exciting market for the sport and Alexander has a great deal of support there, so it is nice to develop new links to that audience. Alexander will be an integral part of the team, immersing himself in our engineering activity so that he is fully prepared should he ever be required to deputise for one of the race drivers."
Rossi raced in GP2 this season for Caterham's GP2 squad, before switching to Campos for a one-off outing in Germany. He will not be participating in the series this weekend.