Seven-time champion Williams was hoping to equal Margaret Court's record of 24 grand slam singles crowns, but was blown away by Halep's blistering display on Centre Court in just 56 minutes.
Halep's French Open triumph last year had helped to lay to rest the demons of three previous Major final defeats and the No.7 seed looked completely at home in her first decider at the All England Club.
Williams was undoubtedly below her best, but the reality was, even at the peak of her powers, she would have struggled to live with Halep's relentless accuracy and energy, the world No.7 committing only three unforced errors.
Her rival, meanwhile, tallied 26 as she fell to defeat in a third straight Major final for the first time in her career, while Halep celebrated the most resounding of triumphs by sinking to her knees and then covering her mouth with her hand, seemingly in disbelief at her own display.
The majestic former world No.1 was a bundle of energy throughout, dictating rally after rally and drawing gasps from the crowd with her astonishing athleticism and skill.
Williams was beaten in straights sets by Angelique Kerber in the final last year and suffered a huge meltdown as Naomi Osaka brushed her aside in the US Open decider two months later.
The 37-year-old looked like she did not know what had hit her again during and after a regal performance with the Duchess of Cambridge and Williams's friend the Duchess of Sussex watching on from the Royal Box.
She was made to look sluggish by a vibrant Halep, who charged around the hallowed turf at rapid speed and never looked back after racing into a 4-0 lead in only 11 minutes.
Williams had a forlorn look of resignation on her face as the sprightly Halep defended as if her life depended on it, winning points she had no right to with incredible court coverage.
"She played out of her mind. It was a little bit deer in headlights for me," Williams said after another chance to match Court's tally passed her by in a flash.