Winson Benta, 59, of no fixed address, was found guilty on Friday of sexual assault, assault occasioning actual bodily harm and committing a sexual offence with intent.
The trial at Reading Crown Court has lasted all week.
The convictions related to an attack on January 30, 2019, when a woman aged in her thirties was knocked unconscious on the grounds of the Slough church.
Benta was arrested on March 6 this year and charged the following day.
He will be sentenced on a date to be confirmed.
Detective Constable Jessica Lawson, of Slough police station, said: “This was a terrible incident, whereby a woman aged in her thirties was approached in dark church yard, knocked unconscious, before being sexually assaulted.
“This was a very long and extensive investigation, and I would like to thank and pay tribute to the victim for her bravery and dignity throughout this process, especially while giving evidence in court and having to relive the circumstances of her horrific ordeal.
“I am extremely happy that Benta has been found guilty in court. He is a dangerous man and a threat to the community.
“He will now receive a sentence in court to reflect this conviction.
“Thames Valley Police will always investigate every report we receive concerning sexual offences, and will investigate thoroughly in order to bring offenders like Benta to justice. Victims will always be listened to and be treated with utmost dignity and respect.”