Ronan was hot favourite to win the coveted award in the weeks leading up to the ceremony, while "Lady Bird" was also thought to be the top contender, alongside horror-comedy "Get Out", for the Best Motion Picture - Comedy award.
She was previously nominated twice. She looked INCREDIBLE! Saoirse always makes a fashion statement on the red carpet, and this year was no different. This time for her performance as Eilis Lacey is Brooklyn.
Beyond the Globes, Ronan has this season received nominations from the SAG Awards-nominated for Actress in a Leading Role, and as part of the film's exceptional ensemble cast-as well as the Film Independent Spirit Awards and Gotham Awards, where she won Best Actress.
London-Irish filmmaker McDonagh also won the Best Screenplay award for his searing study of grief, with two of his stars, Frances McDormand and Sam Rockwell, winning Best Actress - Drama and Best Supporting Actor respectively for their performances.
You could tell that even at the young age of 10, she was destined for stardom.
From her hair and her makeup to her Versace dress and everyone who worked on it - the Best Actress's aesthetic was thanks entirely to the work of fellow women.