The Finnish driver Heikki Kovalainen is Lotus's replacement for compatriot Kimi Raikkonen at this weekend's United States Grand Prix and the season-ending race in Brazil.
Discussions involving both Lotus and Caterham finally reached an agreement, allowing the former McLaren driver to stand in for the Ferrari-bound Finn.
Securing Caterham's blessing for the deal, because Kovalainen is still under contract until the end of the season, was an important element.
Kovalainen has already visited Lotus' Enstone headquarters to finalise his preparations for a return to racing action for the first time since 2012.
Kovalainen's deal came after efforts to recruit Germans Nico Hulkenberg of Sauber and former champion Michael Schumacher, now in retirement, came to nothing.
Raikkonen pulled out of the season's last two races to undergo back surgery.