Anthony Mundine says he will now "sail into the sunset" after losing a split decision to John-Wayne Parr at the Brisbane Convention and Exhibition Centre.
Judges scored the fight 94-95, 96-93 & 95-93 in favour of Muay Thai legend Parr, who was fighting in a boxing ring for the first time in 16 years.
Mundine was knocked down in the fourth round of the middleweight contest but survived a standing eight count before being docked a point in the eighth for hitting Parr in the back of the head.
Although he edged the final round, two of the judges gave the decision to Parr whose last fight was against Sakio Bika in 2003.
The defeat takes Mundine's record to 48-10 and at 44 years of age, with four of those losses coming in his last five fights.
"I've had a wonderful career. I thought I did enough to win, but that's boxing. I'm going to sail into the sunset now," Mundine said after the fight.
"I want to thank all the Australian public. Even if they didn't support me or didn't like my opinions, I always did my best."
Mundine enjoyed several high points, included victories over American Antwun Echols to win the vacant super-middleweight title in 2003 before embarking on a bitter rivalry with Danny Green.
The pair faced off in a memorable event at the Sydney Football Stadium in front of 37,000 fans in what is regarded as the biggest fight on Australian soil.