The Jamaica-born 20-year-old joins the Dutch Eredivisie side on a full-time basis for an undisclosed fee.
Hernes spent last season on loan at Groningen, making 11 appearances in all competitions and helping the club secure a ninth-place finish in the Dutch top-flight.
He joined Newcastle in September 2023 from Shrewsbury Town and scored on his professional debut for the club’s Under-21s team in an EFL Trophy game against Wolves.
Hernes, who represents Norway at youth level, was named on the bench for Newcastle’s FA Cup victory against Fulham at Craven Cottage in January 2024, before featuring in a Premier League matchday squad for the first time during Newcastle’s 3- 1 win over Aston Villa later that month.
A Newcastle statement said: “Everybody at Newcastle United would like to thank Travis for his contribution to the club and wishes him well for the future.”