The jury of eight women and four men reached its verdict after six hours and 10 minutes of deliberation.
The plaintiff Nikita Hand alleged that McGregor sexually assaulted her on Dec. 9, 2018, and that another man, James Lawrence, did the same, Ireland's high court heard during two weeks of evidence.
McGregor denied the allegation and said that he had "fully consensual sex" with Hand. He also denied causing bruising to the plaintiff.
Hand's lawyer told the jury that when she was referred to a sexual assault treatment unit the day after the alleged assault, a doctor was so concerned that he directed that photographs be taken of her injuries.
Hand said that she and a friend made contact with McGregor, who she knew, after a work Christmas party. She said they were driven by McGregor to a party in a penthouse room of a south Dublin hotel where drugs and alcohol were consumed.
She said McGregor took her a bedroom in the penthouse and sexually assaulted her. Hand's lawyer, John Gordon, said Hand was on anti-depressants, and "full of drugs" at the time of the alleged assault.
Speaking outside the court, Hands said she was overwhelmed by the support she had received and that she felt vindicated.
"I hope my story is a reminder that no matter how afraid you might be, speak up," she said.