In January 2006, Bradley became the youngest MLS player to ever be sold when he was transferred to Heerenveen for $250,000 and a portion of any sell-on fee His first start for the Dutch club came on April 16, 2006, in a match against AZ. He found success early, earning five starts and helping the club to a coveted UEFA Cup spot in his first half-season. Upon the retirement of Paul Bosvelt after the 2006–07 season, Bradley took the veteran's starting place in central midfield. Bradley scored sixteen Eredivisie goals and twenty in all competitions during the 2007–08 season.
