Choi is credited with developing the martial art of Taekwondo by combining elements of Oh Do Kwan Karate and Tang Soo Do. He founded the Oh Do Kwan and held a high ranking in the Chung Do Kwan. However, he was stripped of his rank and position due to accusations of dishonesty. In 1955, he officially named his new style "Taekwon-Do," which translates to "foot, fist, art" or "the way of hand and foot."

During the 1960s, Choi and Nam Tae-hi worked to promote Taekwondo internationally, with Choi playing a significant role in spreading the martial art around the world. He is credited with stationing Korean Taekwondo instructors in various countries to help spread the art. In 1965, Choi published the first English Taekwondo syllabus book, titled "Taekwon-Do."

In 1972, Choi went into exile in Canada after the South Korean government objected to his efforts to introduce Taekwondo into North Korea. In response, the South Korean government formed the World Taekwondo Federation (WTF), later renamed to World Taekwondo (WT) in 2018. Despite the controversy, Choi continued to spread Taekwondo globally and in 1979, he defected to North Korea where he was welcomed by the government and supported in his mission to promote Taekwondo worldwide.