It's the second Golden Globe in six nominations for Williams.
She wins it for playing Gwen Verdon, the dancer and collaborator with choreographer and director Bob Fosse whose relationship with him was the basis of the FX show "Fosse/Verdon."
SEE ALSO: Full list of 2020 Golden Globes winners, nominees
In a night that was mostly lacking in political talk despite increasing tensions with Iran, Williams spoke out for women and abortion rights during her acceptance speech.
She said she could not have had her career without employing "a woman's right to choose. To choose when to have my children, and with whom."
"When it's time to vote, please do so in your own self-interest," she said later in her speech. It's what men have been doing for years."
PHOTOS: Golden Globes 2020 red carpet fashion