The former New Zealand captain earned the reputation for being one of the fiercest strikers of the cricket ball and calls time on his career as a legendary figure in the shortest format of the game.
Renowned for hard-hitting skills, McCullum's unorthodox and attacking leadership guided the Black Caps to the 2015 World Cup final where they were beaten by Australia.
Later, McCullum bid farewell to international cricket in 2016 after skippering his side against Australia, managing to smash the fastest century in Test matches in his 101st appearance in the five-day format.
McCullum has since then played the role of a freelance T20 cricketer, lighting up several franchise-based competitions around the world with his aggressive stroke play.
He finishes his career as T20 cricket's second-highest run-scorer, behind Chris Gayle in the distinguished list.
"It is with pride and satisfaction that I am today announcing my retirement from all cricket following the conclusion of the GT20 in Canada," McCullum wrote in a lengthy post on social media.
"As much as I am proud of what I've achieved in my 20 year professional career - more than I could ever have dreamed of when I first entered the game - I have felt the drive to keep going harder to maintain in recent months."
"I look back with pride over the way I've played the game and what I've achieved... I can leave the game knowing I left no stone unturned," he added.
"It's been one hell of a ride but I've always maintained that all good things must come to an end."