Haas, whose car will use Ferrari power, announced Grosjean's signing during a press conference at their United States base in Kannapolis, North Carolina on Tuesday, attended by founder Gene Haas and team principal Guenther Steiner.
“What Gene Haas and everyone at Haas F1 Team is building is impressive, and I’m very proud to be a part of it,” said Grosjean. “Formula One is incredibly competitive and the only way to succeed is by finding new ways of doing things.
"This is a new opportunity with a new team that is taking a very different approach to Formula One. I believe in their approach and they believe in me. While I am committed to giving my absolute best to my current team in these last five races, I am very excited for what the future holds at Haas F1 Team.
“I’ve been at Enstone 10 years and know all the guys there, so it would have been easy to stay, but on the other hand I want to win races and championships and I think coming to Haas is a good step towards achieving that.”
Commenting on Grosjean's appointment, Haas stated: “We wanted an experienced driver capable of developing our car and our race team into one that can score points and better itself each race and each season. We found him in Romain Grosjean.
“I’ve been involved in motorsports for a long time and learned early on the most crucial component is the driver. Romain has strong credentials and he will be an important asset to Haas F1 Team.”
Steiner added: “In addition to being an experienced Formula One driver, Romain is very technically minded. He gives strong, specific feedback as to how the car performs. As we develop our car in testing and throughout the season, his insight will be crucial.”
Grosjean has been a fixture of Lotus’s driver line-up for the past four seasons, having earlier made his F1 debut with the team - in their previous Renault guise - back in 2009. The 29-year-old Frenchman has since scored an impressive 10 podium finishes, including second places in the 2012 Canadian Grand Prix and the 2013 United States round.
His departure at Lotus, who look poised to be once more taken over by Renault, leaves a vacancy alongside Pastor Maldonado for next season, with current test and reserve Jolyon Palmer among the potential candidates to replace him.
Watch: Grosjean's finest moments