From there Fenech had a stellar amateur career, which led to him representing his country at the 1984 Summer Olympics in Los Angeles where he was selected as the boxing team captain.

He became the eighth-fastest boxer to fight for a world title after beginning his career when he challenged Satoshi Shingaki for the IBF Bantamweight title in only his seventh bout, displacing the second Davey Moore, and trailing Shingaki himself, Leon Spinks, Saensak Muangsurin, Pete Rademacher, Joves De La Puz, Joko Arter and Rafael Lovera.

Fenech was the third fastest boxer to become a world champion, behind Muangsuring and Spinks, when he knocked out Shingaki in nine rounds in front of a packed house at the Horden Pavilion in Sydney.

After one more non-title knockout win, Fenech had to go the distance for the first time, when he faced American Jerome Coffee at the Sydney Entertainment Centre, retaining the title by a 15-round unanimous decision.

[3] In 1986, Fenech had only two bouts, but they were both major fights: He won a 10-round, non-title fight decision over former WBC bantamweight and future super bantamweight world champion Daniel Zaragoza, and he retained his IBF world championship with a TKO in round 14 over American Steve McCrory[3] in a bout dubbed "Olympic Revenge" by Fenech's then promoter Bill Mordy.

McCrory, like Fenech, had competed in the flyweight division at the Los Angeles Olympics, winning the Gold Medal by defeating Redžep Redžepovski in the final.

After the bout at the Sydney Entertainment Centre, McCrory graciously allowed the Australian to wear his Olympic Gold Medal to show off to the crowd.

Fenech joined boxing's exclusive group of fighters who have been world champs in three or more divisions, by knocking Callejas out in the 11th round.

The fight was fought on the undercard to the Mike Tyson vs Razor Ruddock rematch at Caesars Palace in Las Vegas.

After 12 ferocious rounds the bout was controversially declared a draw with many of the boxing press who were present (as well as Tyson) claiming that Fenech had been robbed of a clear win.

"[7] On Monday 7 November 2022, a review of the fight by WBC Boxing retrospectively declared Fenech the winner, thus giving him a fourth world title.

This time in front of over 30,000 fans at the Princes Park football stadium, Fenech suffered his first loss, when he was knocked out in the eighth round for Nelson to retain the world title.

In 1996, in what was thought to have been his last fight (he fought Nelson a third time 12 years later), he lost to IBF lightweight champion Phillip Holiday of South Africa by a knockout in the second round.

[12] On 5 January 2004, Fenech was attacked and stabbed by four men in Sydney, receiving facial cuts that required plastic surgery.