The stars, who frequently post about veganism, both wore Yves Saint Laurent to the annual fashion fundraiser, created by designer Anthony Vaccarello.
Cyrus posted to her 92.5 million Instagram followers: "Thank you @ysl @anthonyvaccarello for the custom vegan faux leather platforms! (Liam's shoes are also vegan!)"
While the couple opted for a cruelty-free look, many celebrities, including Naomi Campbell and Cardi B, have been blasted for turning up to the event wearing dresses made of real animal feathers.
Animal-rights organization, PETA, said: "With all those privileged folks in attendance, you’d think the Met Gala could afford a little compassion for one night.
"The fashion world now knows how cruel it is to wear dead animals' fur, but as far as we can tell—with everyone trying to look like Big Bird at the gala—it's still ignorant about where feathers for those gaudy outfits come from."
'Stylish and sustainable'
Last year, Cyrus attended the Met Gala wearing a vegan dress from designer Stella McCartney, showing 'there doesn't have to be torture in fabulous fashion'.
In a brief interview with Vogue Magazine, Cyrus added: "You can be stylish, and sustainable all at the same time."