Leung's father saw an advertisement for a casting call for Harry Potter and the Goblet of Fire and suggested she try out. She waited for four hours in line for her five minute audition. Two weeks later she was called for a workshop and was later offered the part of Cho. More than 3,000 other girls had been considered for the part, including actresses Courtney Webb and Michelle Ang. She stated in an interview with the Daily Record that her Scottish accent probably gave her an edge in the casting.

Daniel Radcliffe, the actor who plays Harry, said that Leung is "awesome" and a "really amazing actress". Her best friend on set was Bonnie Wright who plays Ginny Weasley in the films. Leung delayed plans to go to art college and university in order to film Harry Potter and the Order of the Phoenix. In the film, Leung and Radcliffe share an on-screen kiss, a fact that received much media attention.

When asked whether she will be back for the sixth film, Leung responded, "I don't