The 25-year-old's ranking slumped to 957th after an 11-month absence and a first-round defeat at Wimbledon last year, but she bounced back in stunning fashion by winning the US Open against her close friend Madison Keys - the same player Stephens beat in the semi-finals at Roland Garros on Thursday.
Halep assured herself of retaining the No. 1 ranking and reached her third final in Paris.
"It's great that 40 years after Virginia, I won", Halep said.
"I was dreaming about this moment since I started to play tennis".
Just like she wowed the tennis world with her summer past year, Stephens is enjoying a strong spring that started with her winning the title in Miami.
Halep won 15 of the next 18 points on Saturday, and then 12 of the next 15 games with both strength and steadiness, and she did it against a big-point player who stood 6-0 in WTA Tour finals previously.
Stevens netted a service return to bow out.
The 2008 Roland Garros girls' singles champion learnt a harsh lesson previous year against Jelena Ostapenko, when she played not to lose from 3-0 up in the second set. She also was coming off a lopsided victory in the quarterfinals a day earlier, overwhelming five-time major champion Maria Sharapova 6-2, 6-1.
"I think we are going to have a terrific tussle". She wheeled toward her box, which included US national soccer team player Jozy Altidore, and shook a fist.
Halep's road to her first major was extraordinarily hard, but likewise, this French Open crown represents more of a beginning than an end.
"You feel like there's been so much resilience from Simona Halep having had heartbreak in the final here a year ago where she was expected to win". Stephens is 6-0 in career final appearances and one of those victories came on clay court.
"Not the trophy I wanted", Stephens said, looking at her runner-up plate, "but it's still attractive".
It was the ideal way for the Romanian to banish the demons of her painful final defeat by Jelena Ostapenko 12 months ago, when she blew a lead of a set and 3-0.
Romania's Simona Halep wins the French Open against American Sloane Stephens.
Halep's win led to an outpouring of joy from the tennis world, and her peers and legends took to Twitter to congratulate the newly-crowned Grand Slam champion, as well as heap praise on runner-up Stephens.
Halep struggled to dictate the pace from the back but failed to change pace, to open up the court, to put her opponent out of her comfort zone.
The match was all but ended as Halep clinched the double break in game four after some magnificent defending in one of the points of the match. She won the second set 6-3 and ran away with the decider 6-2.