The 32-year-old actress and her 30-year-old sibling attended the 2016 Screen Actors Guild Awards at the Shrine Auditorium in Los Angeles. Rooney was nominated for Outstanding Supporting Actress for Carol, but lost to Alicia Vikander in The Danish Girl.
Kate and Rooney both turned heads in cleavage-baring Valentino gowns. Kate opted for a shimmering dress with cutout detail and Forevermark diamonds, while Rooney chose a black gown with matching cape and Fred Leighton jewels.
"I don't know if this is sexy by most people's standards, but for me it's more revealing than normal," Kate told E! News, with Rooney adding, "I'm [usually] definitely in sweats. I rarely get dressed, it's really bad. in L.A. you never put real clothes on."
Rooney told E! host Brad Goreski she and Kate chose the same designer "by accident" and confessed her dress wasn't a good representation of who she is. The sisters celebrated prior to the ceremony by drinking champagne.
Kate is known for playing Zoe Barnes on House of Cards, while Rooney portrayed Lisbeth Salander in the American adaptation of The Girl with the Dragon Tattoo. The sisters are often portrayed in the media as rivals, and Kate previously admitted their relationship is "complicated."
"Of course it's complicated," she told the Guardian in 2014. "It's complicated even if you just have a friend who's an actor because the whole business is competition. You're constantly being compared to other actresses and if you don't have a good perspective on that then it can be confusing."
"But luckily my sister and I know that, while it may be both of our passions, it is just a job at the end of the day," she qualified. "It's not the important thing to either of us. It's quite surreal that we both are so lucky in the success of it all."
Kate will star in the sci-fi thriller Morgan with Rose Leslie, and is also slated for an adaptation of The Heyday of Insensitive Bastards with James Franco. Rooney will appear in Una with Ben Mendelsohn and The Secret Scripture with Theo James.