Ryan Cullen has sealed a move into GP3, claiming the final seat at Manor.
The Irish 22-year-old only gained his first full season of single-seater racing last year, competing in the UK Formula Ford EcoBoost class.
He contested the first six races of this year's New Zealand-based Toyota Racing Series, and has also tested in GP3 in 2012 and more recently at Barcelona this year for Bamboo.
Cullen, who will partner Tio Ellinas and Dino Zamparelli in the team, said he will be playing catch-up when the season commences at Barcelona on May 10.
"Lining up on the grid in Spain next weekend will be a dream come true for me, but I am well aware that there is a lot of hard work ahead as I play catch-up with my new team-mates, Tio and Dino," Cullen explained.
"There is a lot I can learn from them as I get up to speed and this is a fantastically supportive team, so I'm in the best possible hands to make my GP3 debut."
Marussia F1 team principal John Booth added: "We are very excited to see our 2013 GP3 series challenge get underway next week in Spain and we will be keeping a close eye on our young drivers from the pit wall.
"We are particularly pleased to see Tio Ellinas back with us for a second successive season and eager to see what Dino and Ryan can achieve as they make their GP3 debuts."
Cullen's confirmation leaves just one seat still open, at Bamboo. Carmen Jorda and Melville McKee have already signed with the GP3 newcomer team.
2013 GP3 Series line-up so far: ART Jack Harvey Facu Regalia Conor Daly MW Arden Daniil Kvyat Carlos Sainz Jr Robert Visoiu Carlin Eric Lichtenstein Luis Sa Silva Nick Yelloly Jenzer Patric Niederhauser Alex Fontana Samin Gomez Manor Dino Zamparelli Tio Ellinas Ryan Cullen Status Jimmy Eriksson Josh Webster Adderly Fong Bamboo Carmen Jorda Melville McKee tba Trident Emanuele Zonzini David Fumanelli Giovanni Venturini Koiranen Kevin Korjus Aaro Vainio Patrick Kujala