The Saltburn star attended the event with his girlfriend, Espresso singer Sabrina Carpenter.
Oscar nominee Keoghan appeared to take inspiration from the Victorian era as he sported an eye-catching look by Burberry, made up of an olive velvet tailored suit and waistcoat, teamed with a ruffled cream shirt with a necktie and a black top hat.
Meanwhile, US star Carpenter wore an Oscar de la Renta black velvet bodice with a voluminous blue satin skirt.
Irish actor Andrew Scott also turned heads on the carpet by showing off his arms in a Versace ensemble, as he walked the red carpet with actor Jude Law and designer Donatella Versace.
Law famously played played Dickie Greenleaf in the 1999 original film version of The Talented Mr Ripley, starring opposite Matt Damon, while Scott played Tom Ripley in the 2024 remake, opposite Johnny Flynn as Dickie.
Northern Irish star Jamie Dornan made his Met Gala debut in a morning suit by Loewe, designed by fellow Northern Irishman Jonathan Anderson.
He teamed a pale blue waistcoat and red tie with a dark jacket and pin-striped trousers.
Anderson was well represented on the red carpet, with a whole host of stars sporting Loewe, including Challengers actors Josh O’Connor and Mike Faist, The Bear star Ayo Edebiri, Past Lives actress Greta Lee, music superstar Ariana Grande, and Waves actress Taylor Russell.
Irish designer Sean McGirr also got a show of support at the Met, with Lana Del Rey sporting one of his looks for Alexander McQueen.
The Video Games singer attended the event with the creative director, wearing a nude corseted dress embellished with hand-embroidered sequinned branches.
She wore a headpiece made up of real hawthorn branches, with swathes of see-through tulle covering her, and a red rose on her hand.
The outfit referenced a look from the autumn/winter 2006 Alexander McQueen collection, which had similar tulle around the model’s head, but held up by ‘antlers’.
McGirr wore a black suit with a satin shirt teamed with black shoes with dramatic oversized leather tassels.