"It's the best chance to be world champion one day," Grosjean told Reuters ahead of the Australian season-opener on March 20.
"I can get a different experience, I can learn more, I can be more ready, you need to get the best car to be world champion. Is it going to be with Haas one day? Is it going to be with another team? I don't know."
Grosjean said he needed a new adventure after effectively spending his entire F1 career to date with one team, and Haas offered it.
The newcomers are seen by many as a Ferrari 'B team', benefiting from a close technical partnership with the sport's oldest and most successful outfit.
With 2007 world champion Kimi Raikkonen out of contract at the end of the season, and the Finn's seat among the most highly coveted, being part of the 'Ferrari family' could be good for Grosjean.
The only driver on the starting grid with experience of the Renault, Mercedes and Ferrari V6 turbo engines introduced in 2014, he would love the chance but says it is just a dream at present.
"The social media was like ‘Ah, Grosjean signed for Haas, he must have a contract with Ferrari signed already'. That is completely wrong," he said.
"Since I was a kid, since I was five, I wanted to drive for Ferrari. Is it going to happen one day? Is it never going to happen? I have no idea.
"It would be a dream. But right now I think the chance I have to live something unique by taking a brand new team ... as close as we can to the top team or top result would be a big achievement."
An eventual return to Renault, former champions returning as a full manufacturer and eager to relive past glories, could be a future option also but for the moment Grosjean is revelling in his new role.
"I want to be the driver that when you go to America everyone is cheering for you because you brought the American flag up there. And you live only once in your life," the Frenchman said.
The dream would be to score points in Melbourne and cement Haas among the mid-field runners. That, said the veteran of 83 Grands Prix with 10 podium appearances, was realistic.
"I think we could potentially be in the points early in the season. From there we need to move from the points to the top five and then to the podium and then the win. It's a long process, how long it is going to take I don't know," he said.
"I think there are the resources capable of doing something like that."
Grosjean's career has had plenty of ups and downs. He made his debut with Renault in 2009 as a stand-in after a race-fixing scandal and returned in 2012 after winning the GP2 support series in 2011.
Branded a 'first lap nutcase' by Australian Mark Webber in 2012 after multiple crashes that earned him a one-race ban, Grosjean used sports psychology to get back in the right frame of mind and is a genuinely quick talent.
Last season the Lotus cars were impounded by bailiffs and the team locked out of paddock facilities with the Frenchman frequently having to hand his car over to British reserve Jolyon Palmer in Friday practice. This year promises stability.
"I think all the experience you have in your life makes you stronger," said Grosjean.
"It was crashes, podiums, difficulties financially with the team ... but here we are ready to have a new adventure and I'll try to lead the team as much as I can."