The star of the films The Illusionist, The Texas Chainsaw Massacre and Next, among others, has joined the singer on his European tour.
Timberlake welcomed the pretty actress to his concerts in Amsterdam and Stockholm this week.
The singer had recently said that he preferred that Biel not join him on tour, so that he could concentrate on his music.
After splitting from Cameron Diaz last year, Timberlake became one of the most eligible bachelors in Hollywood. He began dating Biel after the Grammy Awards.