In 2000, one of the model agencies that Chung worked for as part-time while in HK contacted Chung about a job opportunity offered by Emperor Entertainment Group (EEG). She accepted the offer in 2000, becoming a contracted artist, and underwent training before her debut. She was advised to adopt Chung Yan-tung as a stage name by her manager Mani Fok, after consulting with fortune tellers. The name was supposed to enhance her business abilities. On 18 May 2001, the management company assigned her to form a singing duo, Twins with Charlene Choi. They released their first album three months later.
Chung made her solo-acting film dÃ©but in U Man, which was released in 2002 and has since proven her acting skills in a number of films like Beyond Our Ken which earned her critical acclaim as well as a nomination for Best Actress in the Gam Zhi Ging Awards.
In Beyond Our Ken (2004), Chung played Chan Wai Ching, a spurned girlfriend of the eponymous Ken. The film had its world premiere at the Tokyo International Film Festival and took HK$3,886,355 at the box office. By January 2006, the film 49 Days had exceeded the HK$10 million (US$1.28 million) mark, earning a spot in one of Hong Kong's best box office films for 2006.
On 13 September 2009 Chung showcased an emotional performance art video at the Harbin Ice Snow World carnival singing competition. The silent video, previously filmed in Hong Kong, was shown at the fair lasting 8 minutes 43 seconds. The video showed Gillian Chung switch from laughing to crying. This attraction drew hundreds of visitors each day. Many in the audience thought that Chung used the art expression to reveal her apologetic attitude. However the video was only meant to show how attitudes are expressed through art, according to artist and video creator Jiang Zhi.
On 27 March 2010, Chung released her dÃ©but solo EP, which was sold as part of the package of Twins' fourth compilation album (人人彈起). The EP includes six songs, including dÃ©but solo single More Hearts (心多) that was released a year prior to the album release.