The current Wimbledon and US Open champion produced another powerful display to see off the brave challenge of Russian Elena Dementieva 6-2 6-4.
Her victory saw the United States continue its fine record in the event, following Jennifer Capriati's win in 1992 and Lindsay Davenport's triumph four years ago in Atlanta.
It also extends her winning streak to an incredible 32 matches.
"I worked really hard for this one," a delighted Williams said after receiving her medal.
"I've played five weeks of hard tennis and I've been getting tired - finally I'll admit it."
"With the grand slams there are so many opportunities to win. A gold medal its just once every four years and who knows what might happen between now and 2004.
"I remember watching the Olympics at home as a kid. It was one my Dad's dreams to win an Olympic medal," added Williams, who is coached by her father Richard.
"This is one moment in time for me, my country and my family and my team."
Williams rarely looked in danger of letting gold slip through her grasp, and wrapped up the opening set inside 25 minutes.
One ace in particular underlined the gulf between Williams at her best and the rest of the field.
Fired straight at Dementieva's body at over 103 miles an hour, the Russian only just managed to get out of the way let alone get her racquet to the ball.
Relentless groundstrokes
Dementieva did rally when staring defeat in the face and broke Williams when the American was serving for the match at 5-2.
But Williams was not to be denied, and more relentless groundstrokes off both wings secured victory in her next service game.
She may yet go home with another gold medal, her prospects of an Olympic double depending on how she and sister Serena fare in Thursday's women's doubles final.
They brushed aside fifth-seeded Belgians Els Callens and Dominique van Roost 6-4 6-1 on Tuesday, and face Kristie Boogert and Miriam Oremans in the battle for gold.
Related to this story:
Venus on course for Olympic double
(26 Sep 00 | Racquet Sports)
Williams sets up Dementieva clash
(25 Sep 00 | Racquet Sports)