Just over a year ago Mark Webber described Grosjean as "a first-lap nutcase" as the Lotus driver was involved in several early accidents that almost cost him his race seat for the current campaign.
Over the second half of this season the Frenchman has discovered a new lease of life, with only Sebastian Vettel outscoring him in the last five races in which he has been on the podium four times, including a season-high second in Sunday's United States Grand Prix.
It has been suggested that Grosjean is more relaxed behind the wheel since he became a father earlier this year.
Another idea is that, since Kimi Raikkonen announced he was leaving Lotus to join Ferrari, Grosjean has stepped out of the Finn's shadow and is revelling in the spotlight being placed on him.
With regards to becoming a dad, team principal Eric Boullier said: "I'm not sure he has drastically changed.
"But maybe the final part of the puzzle was needed to acquire the self-confidence he was missing somewhere.
"These kids, until they get that full confidence, anything can be wrong.
"There is huge pressure to be fighting at the front row, fighting in quali and fighting in the race.
"We've always known Romain is super fast, actually maybe too fast, sometimes too fast for his car.
"But having this completeness with his family has helped him reach another level of confidence, and then you see the results on track."
As for Raikkonen's exit, with the 34-year-old now out of the picture completely after undergoing back surgery last week, Boullier added:
"It (Grosjean's form) is a combination of him leaving and his personal life being settled.
"All that has brought him a lot of confidence. That was maybe the kick he needed to take off."
Assessing Grosjean overall, Boullier added: "He is starting to become a damned good driver. I think you can rate him in the top three or four today.
"He started to perform well from Germany onwards. There was still a bit of fine tuning required on his side, but he has had a very fine second half of the season.
"Now he will start next year in a different mood, and we will have a different perspective from him."
Asked whether Grosjean was now secure for next year, Boullier replied: "Yes he is."