The 29-year-old singer-turned-actress, who stars as The Countess in the fifth season of the FX series, showed off some leg in a custom red one-shoulder Brandon Maxwell dress with a thigh-high slit. Her lipstick, nails and strappy platform pumps all matched the dress' bright hue.
Gaga and Kinney, who got engaged earlier this year on Valentine's Day, displayed some major PDA -- like this sweet kiss -- while posing for photographers on the red carpet.
Kinney even turned it up a notch with a not-so-sly butt grab.
ET's Leanne Aguilera caught up with Mother Monster on the carpet and found out all the details about that fabulous frock.
"I really loved this dress," Gaga gushed. "My friend, Brandon Maxwell, made it for his latest collection, and I asked him if he would make it in a bold color for me for the evening, and he said he thought it should be blood red."
But more importantly, does she have a gown picked out for her wedding?
"We don't have a wedding planned yet, but we are so happy and happy to be here tonight together," the singer told ET.
Gaga wasn't the only one who had nice things to say about Kinney. Her AHS co-star, Matt Bomer, is a big fan of the singer’s fiancé. "You know what, he's so profoundly cool," Bomer told ET on the carpet. "He actually was so generous that he was saying to her, 'Don't bring me up in front of the guys, It might make them feel weird.' He's so that cool, that comfortable, and that confident in himself. It's a testament to him. Thank you, Taylor!"
ET also caught up with the show's executive producer, Ryan Murphy, who shared details about what Gaga is like on set.
"The thing about [Gaga] that's amazing is she's the biggest professional in the world," he said. "She's the first on the set. She knows everybody's lines. She greets every crew member with a hug, a hello, and a kiss. The cast is in awe of her, not just because of who she is in the world, but because of her commitment to her craft. She works really hard at it, and she's super brave."
"It's been a great thing to witness, how much of a leader she is," he added.
Within the first few minutes of the pilot, Gaga's character engages in a sexy and bloody foursome, and Murphy admitted that he was very nervous to watch it with her family.
"Her parents are coming, so I'm mortified that they're gonna see a six-minute nude scene," he told ET. "She's a very brave actress, and she's brilliant technically. She's trained. I'm very proud of her and I think people will love her performance.”
"I keep saying she reminds me of a 1940's movie star," Murphy continued. "She has a great elegance and a mystery, and she looks beautiful. She's very, very exciting in that role, and she's revitalized and reimagined the whole show, which is hard to do, but she's done it. I'm very happy about that."
Before the premiere episode airs on Oct. 7, watch the video below to hear more details about AHS: Hotel.