The 34-year-old signs off with 195 NRL appearances to his name across stints with Melbourne and St George Illawarra between 2010 and 2019.
A 28-time English international, Widdop returned home in 2020 to finish his career in the Super League at Warrington, and then Castleford.
View this post on Instagram A post shared by GARETH WIDDOP (@garethwiddop)
"All feels a little surreal writing this however all good things come to an end, after much thought and deliberation my time playing Rugby League professionally is up," Widdop wrote on Instagram on Thursday (AEDT).
"I am looking forward and hoping to embrace this next chapter.
"For now taking some time out and see where this life takes me!"
Widdop became a fixture at Melbourne in the aftermath of the salary cap breaches that forced a roster upheaval.
In an era when the club boasted such superstar players as Billy Slater, Cameron Smith and Cooper Cronk, the Englishman held his own.
Widdop started in the Storm's 2012 premiership victory, a 14-4 grinding defeat of Canterbury that was the club's first title since being stripped of the 2007 and 2009 trophies.
Born in Halifax, Widdop can lay claim to being one of few English backs to truly make a mark on Australian rugby league during the NRL era.
He is the only English playmaker to have won either Dally M halfback or five-eighth of the year in the NRL era, picking up the five-eighth award in 2017.
Widdop joined St George Illawarra for the 2014 season, became captain in 2016 and was five-eighth the last time the embattled club played finals in 2018.
Widdop played his last professional game for the Castleford Tigers in round 25 of the most recent Super League season.
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