It will be the Frenchman's fourth straight season with the Enstone-based team, which is switching from Renault to Mercedes power next year.
Grosjean has claimed nine podiums for Lotus since 2012, recording a best overall finish of seventh in the drivers' championship in 2013. This year has proved more challenging however, yielding just two points finishes over the opening 18 Grands Prix.
"It's fantastic for me to be continuing with Lotus F1 Team for 2015 and it's superb to have the support of everyone at Enstone," Grosjean said. "It's no secret that we've had a really tough season this year, but the team has remained focused and we're all determined to return to regular points-scoring in 2015.
"I have been spending a lot of time recently at Enstone and I'm feeling very positive about the potential of the E23, which should represent a return to form for the team. We have one race left in 2014 so I'll be pushing to do the best job possible in Abu Dhabi before my focus switches fully to 2015."
Lotus co-chairman and team principal Gerard Lopez said he was delighted to retain Grosjean for the 2015 season: "It is with great pleasure that we can formally confirm that Romain Grosjean will continue with Lotus F1 Team alongside Pastor Maldonado next season," he said.
"You really learn something about a driver when they have the chips against them and Romain has delivered impeccably in 2014 despite the very big challenges he has faced. We know that Romain will always get the most out of the car at his disposal, which is why we can't wait to harness his potential with Mercedes-Benz power in 2015."
Lotus confirmed in July that they would retain Maldonado for the 2015 campaign. The Venezuelan scored his first points of 2014 in the recent United States Grand Prix.