Klien was BMW reserve driver in 2009 after spells with Jaguar and Red Bull
Austrian Christian Klien has joined Hispania as their second test driver and will take part in first practice at the Spanish Grand Prix this weekend.
Klien, 27, has raced in F1 for both Jaguar and Red Bull and has been a test driver for Honda and BMW Sauber.
He will replace regular driver Karun Chandhok in Friday's first practice session at the Circuit de Catalunya.
"As a young team we are looking for drivers who can grow with us," said Hispania boss Colin Kolles.
"We look forward to having Christian alongside us in Barcelona later this week so he can spend some valuable familiarisation time with the team."
Klien, who will take part in a race weekend for the first time since the 2007 British Grand Prix when he replaced Jenson Button in second practice at Silverstone while at Honda, is eager to impress his new boss.
"This role offers me the opportunity to rejoin the Formula 1 environment and drive again, which is naturally where my longer-term ambitions lie," said Klien.
"My goal was always to get back into F1, so I feel a lot of satisfaction that I can still be hired as a grand prix driver for my speed and skills.
"That is proof enough of Colin Kolles' faith and trust in me."
Between 2004 and 2006 Klien raced for Jaguar, staying on when the team was taken over by Red Bull.
In 2007 he was test driver for Honda and was then BMW's reserve driver until they quit the sport last year.
Spain-based Hispania, who are the renamed former Campos team, are one of three new outfits on the grid this season, along with Lotus and Virgin, and all three are yet to score any points after four races.
Hispania have two inexperienced drivers in Indian Chandhok and Brazilian Bruno Senna, who are both 26 and each made their F1 debuts this season in Bahrain.
Team boss Kolles has been looking to add more experience to his team and signed Japan's Sakon Yamamoto as test and reserve driver last month.