Van der Garde, 26, will take part in pre-season testing and a number of Friday first free practice sessions once the championship starts in Australia on March 18.
"He is a very exciting prospect that we have been monitoring since the early days of our team," said principal Tony Fernandes in a statement.
Caterham, whose race drivers are Italian Jarno Trulli and Finland's Heikki Kovalainen, competed as Team Lotus last year and Lotus Racing in their debut season.
Van der Garde finished fifth overall in the GP2 series last year but has been knocking on the door of Formula One for some years with little success.
He was named as both Super Aguri and Spyker tester in 2007, triggering a legal tussle for his services, and was also a Renault development driver. — Reuters
