She joins some of the greatest players in the women's game to achieve the feat.
Maureen Connolly Brinker, Doris Hart, Shirley Fry Irvin, Margaret Court, Billie Jean King, Chris Evert, Martina Navratilova, Steffi Graf and Serena Williams are the other holders of the Australian Open, the French Open, Wimbledon and the US Open during their respective careers.
Italy's Errani fought gamely against the heavier-hitting Sharapova, but did not possess the power to trouble the towering Russian player, who returns to number one in the rankings courtesy of her rise to the title on the Paris clay.
Sharapova wins her fourth Grand Slam title eight years after winning her first at Wimbledon in 2004. She lifted the US Open in 2006 and the Australian Open two years later.
Errani - who claimed he women's doubles title with fellow Italian Roberta Vinci a day earlier - will be happy she did not buckle in the face of Sharapova's baseline bullets having lost the first four games of the match in just over 10 minutes as a final mismatch seemed to be on the cards.
Despite the one-sided scoreline and the sense of inevitability that infiltrated the final, Errani troubled Sharapova with some cute volleys, sliced forehands, daring dropshots but still found her opponent to be an insurmountable obstacle.
With Errani standing at just 5ft 5in and Sharapova over 6ft, the statuesque Russian used her height and wider wingspan to great effect as she chased down everything the Italian could throw at her.
She wrapped up victory when Errani ended a prolonged rally by dumping a backhand into the net before accepting the adulation of the packed crowd amid the Russian national anthem blaring out into a greyish sky.
The victory capped a remarkable comeback for Sharapova after many thought her career was all but over when she underwent shoulder surgery in 2008.
Having waited four years to climb back into the grand slam winner's circle, it was little wonder the 25-year-old dropped to her knees and covered her face in disbelief in her moment of triumph.
But this was no time for the queen of women's tennis to hide her face.
A beaming Sharapova, still on her knees, tilted her head skywards and lapped up the applause from the hollering fans with outstretched arms.
Even when the on-court announcer accidentally asked the crowd to cheer for "runner-up Maria Sharapova", the smile could not be wiped off her face.
Errani, who had been left sobbing after her remarkable fortnight ended one victory short, pumped her arms as if to say "Yes, Yes, Yes, I am actually the champion". During the 89-minute contest though, there was only one winner.
"I'm really speechless. It's been such a journey for me to get to this stage," Sharapova said during her victory speech during which she showed off her multi-lingual skills by speaking in English, French, Spanish and Russian. "It took me many years to get to this stage, eight years ago was my breakthrough.
"I'm so happy to share this moment with you all. I cannot wait to be back. To be here and win this, even if it was my only grand slam, it would be just as special as if it was my fourth."
Errani, bidding to become the lowest seed at 21 to win the title in the professional era, was in danger of suffering a whitewash when Sharapova sprinted out of the blocks.
But just when the fans thought they were about to witness the first whitewash since Steffi Graf beat Natasha Zvereva 6-0 6-0 in the 1988 final, Errani started to produce the kind of shots that helped her to knock out three grand slam champions here.
She raised a huge roar in the stands when she broke Sharapova in the fifth game and then caught out the Russian with some cute angled volleys and delectable dropshots.
Errani also dragged Sharapova into rallys often extending to over 20 shots, and the Italian even managed to dodge two set points on her serve in the eighth game.
Sharapova smacked a service return into the net on the first and could only watch in wonder as Errani drilled a spectacular forehand winner on the next.
However, the Russian second seed was determined to live up to her top billing and won the set on the next game by belting a backhand winner down the line.
The second set started like the first, with Sharapova breaking before romping to a 4-1 lead. But the Italian was determined not to go out without a fight and remained undaunted even when Sharapova brought up her first match point by hitting a brilliant forehand on the run.
She forced Sharapova into a forehand error to get back to deuce, then earned a break point by snaring Sharapova with a dropshot.
Sharapova hit back with a thunderbolt backhand winner and after seeing another matchpoint evaporate with yet another Errani dropshot, she brought up a third with an ace.
This time she made no mistake.