The 21-year-old from Bay of Plenty added the cruiser class (larger diameter wheel size) title to her elite world title victory 24 hours earlier on the indoor track at the Adelaide Showgrounds.
Walker shook off the devastation of her Olympic Games fourth placing to dominate the field in both events over the weekend.
Yesterday she won all three qualifying motos, her semifinal and the final in a brilliant display to complete her set of world championship medals.
She won the silver in 2007 in Canada and the bronze last year in China.
Walker, who choked back tears after just missing the Olympic podium in Beijing last year, said the major difference was a new-found belief in her own ability.
"That's by far the best I have ever ridden," Walker said.
"It's the first time that I have believed that I could do it. I have probably had the skill and ability to win in the past but I have not believed enough in myself.
"I've trained really hard for the last few months, and have been really strong in the gym. As soon as I rode the track I was feeling my bike and was at one with it. I just had confidence that I had the ability and I had done the work."
In yesterday's elite final she beat France's Eva Ailloud by more than a second, with Arielle Martin of the United States third.
Walker said the dominance of her victory yesterday on the tight indoor track was the most satisfying.
"I absolutely nailed it. I won every lap today and was faster than anyone else in every round. You have got to be happy with that."
Her only disappointment was that last year's champion Shanaze Reade of England and Beijing silver medallist Laetiita Le Corguille were missing with injury.
"Some might say that this win was soft because they were missing. I would have loved to have had them here because I was riding that well I believe I would have still won and won really well.
"I won every race easily and my times were pretty fantastic throughout the day."
BikeNZ high performance director Mark Elliott hailed Walker's performance, and praised the efforts of head coach, Canadian Ken Cools.
"Ken has always said that Sarah is the most gifted BMX rider in the world," Elliott said.
"He has stuck to getting the basics right with Sarah instead of looking for a change in approach."
The only disappointment was with Beijing Olympian Marc Willers who crashed in his quarterfinal after he was squeezed around the second corner on the narrow track and came down in a melee at the back of the pack.
Willers said he was disappointed he did not get a better snap from the gates after starting well in all his previous races.
"That left me in the pack for the first corner which is always a problem in this field. I will now look towards a build up for next year although I will have surgery on my injured shoulder," Willers said.
Auckland's Alexandra Williams finished a creditable sixth in her first world championship final.
