Calzaghe, a southpaw, began boxing at age nine.In more than 12 amateur contests, he won four schoolboy ABA titles, followed by three consecutive senior British ABA titles (British Championships) between 1990 and 1993. This made him only the second boxer in history to win in welter, light-middleweight and middleweight divisions. He reportedly had an amateur record of 110–10. Calzaghe received his last defeats at the hands of Michael Smyth in the 1990 Welsh ABA final and Romanian amateur Adrian Opreda at the 1990 European Junior Championships in Prague.Calzaghe was signed up and made his professional debut at Cardiff Arms Park on the Lennox Lewis vs. Frank Bruno bill the following month. By June 1995, Calzaghe had won nine out of nine fights, seven in the first round and two in the second. At the end of 1995 Calzaghe was voted Young Boxer of the Year by the Professional Boxing Association and the Boxing Writers' Club, with Barry McGuigan's top tipping Calzaghe for 1996: "He punches ferociously, moves superbly and has the best of the European technique and US aggression."In October 1995, Calzaghe won the vacant British super middleweight title, stopping Steve Wilson in the eighth round. He successfully defended his title with an easier-than-expected fifth round stoppage of the undefeated puncher Mark Delaney. Calzaghe's critics said that he had not really been tested. Calzaghe said in reply that he could only beat whoever was out there and prepared to fight him.
In November 1996, Calzaghe moved to Frank Warren's stable. Warren, who had managed Nigel Benn for his first twenty fights, declared: "Joe Calzaghe is a far better prospect, in fact he is my fighter for the new millennium." Warren spent the summer of 1997 chasing a fight for Calzaghe with either WBC champion Robin Reid or WBO title holder Steve Collins. The fight with Collins was arranged, but at a late stage Collins withdrew because of injury, was stripped of his title, and then retired.
Calzaghe split with promoter Frank Warren in June 2008 and announced that he would promote his fights personally for the remainder of his career. The split caused Warren to launch a court case against Calzaghe, claiming that a verbal promise to promote the Roy Jones Jr fight was broken and that Calzaghe owed him $1.4 million; Calzaghe in turn claimed that Warren owed him past fees. In March 2009 the High Court ruled that Warren had persuaded Calzaghe to sign contracts under duress when Calzaghe was hungry and dehydrated preparing for matches and that Warren's company Sports Network Limited owed Calzaghe $2.8 million in unpaid fees. Sports Network Limited intends to appeal the award.