The 32-year-old boy band star was accused of attacking the woman in a hotel room following a solo concert in December. He said they had consensual sex.
They jury, of eight women and four men, deliberated for around two hours before unanimously acquitting Williams.
His tour manager Jamien Nagadhana, 32, who was sleeping in the same room, has been cleared of charges of sexual assault and assault by penetration. He admitted to touching the woman briefly as he tried to initiate a threesome.
Williams, from Croydon, south London, met the woman at the nightclub he had performed at.
The singer called the allegation of rape "crazy" and said he was left "bewildered" by the claim in police interviews read out during the proceedings at Wolverhampton Crown Court.
Responding to the alleged victim's account, Williams told officers: "C'mon, this is crazy. I am very perplexed, to be honest with you.
"I am feeling bewildered at this whole thing. I do feel taken advantage of. I just feel like a musician, an artist that has been put into a position where they have been taken advantage of."
During the trial, Williams said he had a consensual encounter with the complainant, which ended in embarrassment when he was "unable to perform" sexually.
Nagadhana declined to comment in an interview with police, but submitted a prepared statement which alleged he had kissed the woman and touched her but had backed off when he realised she was "getting together" with Williams.
Prosecutors said the woman and her two friends had felt "a lot more affected by alcohol than they felt was normal" and one had to be put in a taxi home after she "blacked out".
The woman and her other friend then went back to the hotel with Williams and Nagadhana, where she said she was pushed on to the bed after making it clear that she didn't want to have sex with him.
She told an interviewing police officer: "I was quite scared. I felt more pathetic, if that makes sense. I just felt worthless."
The woman told jurors she had a "bits and pieces" memory of her night after drinking Malibu, sambuca and shots but said: "The memories I do have, I know took place."
Defending Williams, his lawyer accused the woman of having selective memory loss and said: "There is no realistic answer as to why he would do it."