Halfpenny was originally a member of the Ospreys academy who let him go because of concerns about his size.
He signed for Cardiff Blues ahead of the 2007-08 season and played for Cardiff RFC and the then Cardiff Blues between 2007 and 2014.
"I'll be forever grateful to Cardiff for giving me the opportunity to join the academy and start my professional career," said Halfpenny.
"I instantly felt at home and will always look back at my time at Cardiff as some of the most memorable years of my life."
During that seven-year stint, Halfpenny made 87 appearances and scored 568 points, winning the Amlin [now European] Challenge Cup and [now defunct] Anglo-Welsh Cup.
He signed for Toulon in 2014, winning the 2015 European Champions Cup with the French side before returning to Wales with Scarlets in 2017, spending six seasons in Llanelli.
Halfpenny travelled to New Zealand to join Crusaders in 2024 before linking up with Harlequins the following year.
After being involved as a kicking coach for Wales' summer tour of Japan in 2025, Halfpenny returned to Cardiff with a short-term contract in September 2025 as a kicking coach and player and that deal was extended until the end of the season.
He played his first game for the Blue and Blacks in 4,347 days when he faced Ulster in the win in December 2025 and also featured against the same opposition the following month.
That appearance off the bench in Belfast during the 21-14 defeat could be his final professional match, if Halfpenny is not involved in Cardiff's two remaining United Rugby Championship (URC) matches against Glasgow and Stormers or any further play-off games.
"It's a special club and to be able to finish my playing career where I started means so much," said Halfpenny.
"I have given everything to rugby, and in return, it's given me more than I could ever have dreamed of.
"It's never going to be easy to say goodbye but I'm finishing with an immense sense of pride and gratitude."