Jurors at Wolverhampton Crown Court deliberated for around two hours before unanimously acquitting Williams, who told the jury he had consensual sex with the woman in the city in December 2016.
A jury of eight women and four men also cleared Williams' tour manager, 32-year-old Jamien Nagadhana, of two sexual assault charges relating to the same woman.
The prosecution had alleged Williams, also 32, tried to have sex with the woman, who cannot be named, and then raped her when she returned to his hotel room to look for her belongings.
The singer, from Croydon, south London, told his nine-day hearing that he had a consensual encounter with the complainant, which ended in embarrassment when he was "unable to perform" sexually.
The former boy band member's defence lawyer suggested the woman's complaint to police was influenced by the "extreme reaction" of her friend to being told of the consensual encounter.
Nagadhana, from Hounslow, west London, told the court he touched the woman in a bid to start a three-some, reasonably believing she was consenting.
The trial was told Williams had met the woman at a meet-and-greet event at a nightclub.
His barrister, Mark Cotter QC, claimed during his closing speech that the nightclubber had a selective memory around "tricky" aspects of her account.
Addressing jurors on the seventh day of the trial, Mr Cotter described the woman's assertion that she could remember sitting on Williams's lap at the club as "the understatement of the year".
Referring to CCTV from the venue which showed "three-way" kissing and the complainant and two female friends behaving in a raunchy, sexual way, Mr Cotter said of the footage: "Right at the end (the alleged victim) is on top of Oritse Williams.
"When she and Oritse Williams are standing outside the club, you may think they look for all the world as though they are a couple."
Concluding his speech, Mr Cotter said of the rape allegation: "There is no realistic answer as to why he would do it.
"There is plenty of evidence, we suggest, that something happened between them and that the description given to the police at the time (by the alleged victim) is not true and accurate."
In his evidence, Williams said the woman had asked to spend the night with him and thanked him when they parted company.
The singer added that the woman had pulled him out of the nightclub after initiating a "highly sexually charged" display in the venue's VIP area.
Saying he had got on very well with the woman and her friends at the club, he told the jury: "You don't forget three girls 'grinding' you all at the same time - you don't need CCTV footage to remind you of that."
Williams declined to answer reporters' questions as he left court.