They earned critical acclaim and two Golden Globe Award nominations for playing the lead role of Rhaenyra Targaryen in House of the Dragon.

Writing for The Arts Desk, Aleks Sierz praised D'Arcy's performance as well as the production's "marvellous moments of wry humour and acute emotional insight.

"[13] In 2018, D'Arcy returned to the Arcola Theatre to portray Lucrezia in Hal Coase's adaptation of Virginia Woolf's Mrs Dalloway.

[16] D'Arcy made their television debut as Naomi Richards in Nick Payne's 2018 BBC One and Netflix series Wanderlust.

[5][17][18][19] In December 2020, it was announced that D'Arcy had been cast as Rhaenyra Targaryen in the HBO fantasy series House of the Dragon, a Game of Thrones prequel and adaptation of George R. R. Martin's companion book Fire & Blood.

"[24] The importance of the role led to D'Arcy being placed under much scrutiny, particularly after Milly Alcock's rendition of the character in her younger years had been positively received.

Club, critic Jenna Scherer wrote, "It's impossible to look away whenever D'Arcy's expressive face is in the frame; even when the show itself drags, they electrify every scene they're in.

[30] Writing for Comic Book Resources, Philip Etemesi pointed to D'Arcy's strong theatre background as the reason for their "expert handling of such a complex character.

[34][35] Out magazine's Mey Rude stated, "D'Arcy has stepped up to the plate in a role that would make most actors stagger, and has become an instant star in doing so.

[49] Also, in 2024, D'Arcy was included on InStyle's Breakthrough list of "30 Performers Defining Culture Now", credited for disrupting the status quo by blurring the lines between traditionally masculine and feminine styles.