The tennis pro co-chaired the event in 2019.
Serena, who co-chaired the Met Gala in 2019 with Lady Gaga, Harry Styles and Gucci creative director Alessandro Michele, arrived on Monday wearing a chic bodysuit and elaborate feathered cape by Gucci.
"It definitely took me a while ... a couple hours," she told reporters on the red carpet of pulling her "super hero"-esque look together. "It's a whole other outfit underneath."
Serena took to Instagram earlier on Monday to preview how she was getting ready for the big ball -- alongside her daughter, Olympia.
The 4-year-old hilariously called her mom a "monster" as she gave her skin a little extra moisture with a hydrating mask. "She can't call me a monster now," Serena said on her Instagram Story as she got her makeup done. "It looks like the mask worked."
Serena's sister, Venus Williams, was also at the Met Gala, and told ET's Rachel Smith that she did not get ready with her sibling.
"We did not [get ready together]. I didn't know what she was wearing, and I wanted it to be a surprise," she shared. "She doesn't know what I'm wearing either."
Venus looked stunning in a red Prabal Gurung gown and fun up do hairstyle.
This year's Met Gala theme is "In America: A Lexicon of Fashion," an exploration of the nation’s sartorial identity and a deep dive into American ingenuity. According to the press release, the exhibition opens Sept. 18 and will highlight "everything from the luxe ease of Halston's '70s glamour to Rodarte's ethereal edge and Kerby Jean-Raymond's powerful political vision for Pyer Moss."