Cleverly made his professional debut in July 2005 with a four round victory over journeyman Ernie Smith at the Meadowbank Sports Center in Edinburgh and within a year had compiled a winning ledger of 6–0. His first fight of substance however was in October 2006 when he met Liverpool's Tony Quigley at the MEN Arena in Manchester. The fight which was on the undercard to the match up between Joe Calzaghe and Sakio Bika ended in a 5th round stoppage for Cleverly and handed Quigley his first pro defeat. The next big test for the young prospect took place at the Millennium Stadium in Cardiff just over a year later in September 2007 when Cleverly met tough Ugandan Joey Vegas. Cleverly at that time boasted a record of 10–0 and Vegas 10–1. The fight ended with a gruelling points win over 8 rounds for the Welshman in what was his toughest fight to date. Speaking about the result to the BBC and referring to the sparring he received in the Enzo Calzaghe gym, Cleverly said "I'm still young and won't be hitting my peak for about eight years, but think how good the wars I'm having in the gym now are doing me for the future ... I want to keep on progressing, to go for the British title, then maybe a world crown in a couple of years."
Cleverly had made a point of fighting on the undercards of his stablemate Joe Calzaghe with the Vegas fight being one of the prelims to Calzaghe's World title unification fight against Mikkel Kessler. The next stop however was the real Vegas, Las Vegas to support Calzaghe's attempt to win The Ring{['}}s Light heavyweight belt against American fighter Bernard Hopkins. Cleverly, fighting outside the UK for the first time as a pro also faced American opposition and beat Antonio Baker over 8 rounds.
In September 2008, the young boxer chose to leave Enzo Calzaghe's Newbridge boxing club where he had trained throughout his career and begin training at his father's gym in South Wales. Speaking about his decision to leave the gym Cleverly said "I have been trained by Enzo Calzaghe for six years since my youth days so leaving him has been one of the hardest decision I've ever had to make ... Enzo is largely responsible for where I am in my career and I cannot thank him enough for what he has done for me." Cleverly had been concerned following the legal wranglings between promoter Frank Warren and his former stablemate Joe Calzaghe and added "I cannot take any chances with my career ... I take boxing very seriously and want to be world champion. Hopefully Frank can sort that out for me."