Heikki Kovalainen is to return to Caterham with immediate effect in the role of reserve driver.
Kovalainen was dropped by the Leafield-based marque after last season as Caterham opted to head down the pay driver route, initially taking on Charles Pic from Marussia before promoting reserve Giedo van der Garde.
That left Kovalainen, who had been in Formula One for six seasons - with the last three of those with Caterham in its various guises - out of work.
But with Caterham struggling at the back of the grid this season, as they have even fallen behind rival tailenders Marussia, Kovalainen has been asked back to help develop their car.
The Finn returns to the track on Friday for first practice for the Bahrain Grand Prix, and will also get behind the wheel for the opening session in Spain early next month.
"It's obviously great news I'll be on track in Bahrain and Spain and I'm really looking forward to getting back to work and helping the team as much as I can," said the 31-year-old.
"I'll be taking part in the two FP1 sessions to give the team my input on the new parts we're bringing to those races.
"I'll also be working closely with the race drivers and the engineers on track and back at Leafield to help everyone get the most out of the new package.
"I'm physically ready to get back into the car. I know my experience can help give the team new ideas and options for directions to take on set up and strategy."
Current reserve Alexander Rossi moves across to Caterham Racing to compete in this year's GP2 championship in the car raced by Ma Qing Hua at the season-opening race in Malaysia.
Caterham claim Ma, who last Friday became the first Chinese driver to take part in an FP1 session in his home country, remains a core member of their team, with an announcement to be made in due course with regard to his revised race plans.
Assessing the changes, team principal Cyril Abiteboul said: "Heikki returns to track work with us and we are delighted to welcome him back into the team.
"He has six years of F1 experience behind him so he is perfectly placed to provide us objective feedback on the various types of configurations we will run and to give us an objective view of the 2013 tyres against his experience with the 2012 compounds.
"Having invested in Heikki for our first three years of competition it would be a waste not to leverage the valuable expertise he brings.
"As F1 is a team sport, he will also provide support to Charles and Giedo, who are both doing a good job in their first months with the team."