Williams was undone by 26 unforced errors to Halep's two in a personal horror show on Centre Court.
"She played out of her mind," said Williams. "I was like a deer in headlights."
Williams, who has now lost three Grand Slam finals since returning to the Tour last March following the birth of daughter Olympia in September 2017, was short of ideas and the match ended after 56 minutes when she biffed a forehand into the net -- her 26th unforced error.
Simona Halep is the first Romanian woman to win in the Wimbledon title