The Russian-backed, British-based team, in their first season in the series after taking over Virgin Racing, have yet to score a point and did not have a reserve driver until they appointed the 21-year-old Briton on Thursday.
In July, test driver Maria de Villota, who does not possess the super-license required to act as a reserve, crashed heavily while performing aerodynamic tests prior to the British Grand Prix and lost her right eye as a result of the accident.
In the previous race at Valencia, Marussia were only able to get Charles Pic on the starting grid after his team mate Timo Glock fell ill on the eve of the grand prix and was unable to take part in qualifying.
The 21-year-old Chilton has been promoted from Marussia's feeder team in the GP2 series, in which he currently lies fifth, and is looking forward to making the step up to Formula One.
"I feel like my racing has really matured this season and to now be able to combine that with real insight into the engineering activities of an F1 team really moves my career onto the next level," he said.
Chilton will join up with the team at the Japanese Grand Prix in Suzuka on October 7.