His films, often made in collaboration with the same group of actors, screenwriters and cinematographers, frequently explore themes of friendship, fate and the changing face of Hong Kong society. Sometimes described as "multifaceted and chameleonic" due to his ability to switch tones and genres between movies, To is nonetheless seen as having a consistent style, which involves mixing subdued realism and social observation with highly stylized visual and acting elements.
While working as an assistant TV director during the Shaw Studios era, he directed All About Ah-Long in 1989, starring Chow Yun-fat, the film became one of the biggest box office hits in that year. In 1988, he co-directed The Big Heat, his first action movie. The film was produced by Tsui Hark. The end of the 1980s also saw some of To's biggest commercial successes, the vast majority of which were comedies. His 1988 film The Eighth Happiness was that year's highest grossing movie.
Commercially successful in his native Hong Kong, To's films have regularly appeared at international festivals, most notably in Europe and North America. Six of To's films have been featured at the Cannes Film Festival: Breaking News premiered as an Out-of-Competition midnight screening in 2004;Election was shown in Competition in 2005; its sequel, Election 2 (aka Triad Election) was screened in Out-of-Competition midnight screenings in 2006, and Triangle was screened in Out-of-Competition midnight screenings in 2007; Vengeance competed for the prestigious Palme D'Or in 2009; Blind Detective was screened in Out-of-Competition midnight screenings in 2013.