The star took home the prize for her role in Big Little Lies in which she played a woman in an abusive relationship.
As she accepted the award, she paid tribute to the "power of women," and to her mum, who she says was an advocate for women's rights.
"Because of her, I am standing here. My achievements are her achievements," she said.
Stars wear black
Turning the Globes dark on the fashion front had been anticipated for days after a call for massive reform following the downfall of movie mogul Harvey Weinstein and numerous others accused of sexual misconduct in Hollywood, media, fashion, tech, publishing and other industries.
Oscar-winning actress Meryl Streep, accompanied by domestic violence advocate Ai-jen Poo, said she chose black to stand in solidarity with others trying to right the power imbalance that leads to sexual abuse.
The new initiative Time's Up, backed by more than 300 women in Hollywood, doled out badges intended in part for those who might already have locked in more colourful looks.
