Tombazis, who joins the team with immediate effect, has a prestigious history in the sport, having served as chief aerodynamicist at Benetton, Ferrari and McLaren over the past 23 years. He has spent the last nine years as Ferrari's chief designer.
"I am very happy to be joining the Manor F1 Team at this exciting time in its development," Tombazis said.
"The team has impressive plans and is investing in all the right areas to achieve its on-track ambitions, so I am very much looking forward to being part of that journey.
"The existing design team is already very strong and I look forward to working with a great group of people to make the most of the opportunities that lie ahead to help us progress through the field over the next few seasons."
Tombazis will work under the leadership of technical director John McQuilliam, who hailed the new appointment. "I believe this will help to amplify the efforts of a very talented design team that, in recent years, has not had the opportunity to showcase the full extent of their experience and capabilities," McQuilliam said.
"I am confident that, together with our new Mercedes power unit and Williams gearbox and technical partnership, our new aero structure will provide us with the strength to design and develop consistently competitive racing cars to help steer us towards our long-term ambitions."
Marussia, who are yet to reveal their driver line-up for the 2016 season, experienced a staff shake-up at the end of last year following the departures of team principal John Booth and president and sporting director Graeme Lowdon, and the arrival of Dave Ryan as racing director.
However, the team remain on course for the first pre-season test of the year in Barcelona on February 22, having successfully completed the final crash test on their now fully homologated new chassis.