Dahlberg plays as a goalkeeper for IFK Göteborg and the Sweden national team. On 31 January 2018, Dahlberg signed for Watford on a 5.5 year deal for an undisclosed fee. He was loaned back to IFK Göteborg until the end of the 2017–18 season. In August 2021, Dahlberg joined Doncaster Rovers on a season-long loan deal. In 14 January 2022, Dahlberg was recalled from his loan spell at Doncaster Rovers and loaned to Gillingham for the rest of the season. Dahlberg made his debut for Sweden national football team on 7 January 2018 in a friendly 1–1 draw with Estonia.