He is best known for collaborating as an associate director for films made by Johnnie To and Wai Ka-Fai of Milkyway Image.
Law began working for Johnnie To as an assistant director at TVB Studios in 1990.
Later, when To left the TV studio, Law continued to work as a director there for three years.
In 1997, Law was recruited by To to join his company, Milkyway Image, where he began to work as an assistant director for To.
Law made his directorial debut with a segment in the horror omnibus Ghost Office, followed by the cat-and-mouse thriller Running Out of Time 2 which won him an award for Best Film Editing at The 39th Golden Horse Awards.