She performed as the opening act on Bruno Mars' 24K Magic World Tour in October and November 2017. In December, it was announced that Smith would be the recipient of the Brit Critics' Choice Award, to be presented at the Brits nominations launch on 13 January 2018. She is the first independent artist to have been nominated for the award, let alone win.
In January 2018, she released the single "Let Me Down" featuring rapper Stormzy. Smith co-wrote and performed the song "I Am" on Kendrick Lamar's soundtrack album for the film Black Panther, released in February. Later that month, she performed at the BRIT Awards with Rag'n'Bone Man. In April, she made her US television debut on Jimmy Kimmel Live! with a performance of "Blue Lights". Her debut studio album, Lost & Found, written over a five-year period, was announced in April and released in June 2018 to critical acclaim. In the month of the album's release, Smith began touring in support of the album, with dates scheduled across Europe and festival appearances in Japan. The Lost & Found Tour's North American leg began on 19 November in Seattle and conclude on 19 December in Toronto and will be supported by Ravyn Lenae.