She was born in Hong Kong and studied at Heep Yunn School and the Australian International School. After her graduation, she began modelling jobs until she was invited to be a singer. She took singing lessons from veteran singer Teresa Caprio. She signed a record deal with Go East Entertainment and a management contract with Starz People. In 2003 she made her debut with the single “Grown Up” 成人對待. She released her EP Grown Up on 27 November 2003. She released her first studio album Step by Step on 24 September 2004 promoted by lead single Red Flower Club 紅花會. She returned the next year with the album Beat Beat, released 18 October 2005.

In 2006 she signed with record label East Asia Music 東亞唱片. The album Honey was released on 9 November 2006, preceded by the release of chart-topping single, “Traffic Light”. The song reached number one on all four major Hong Kong stations (903, RTHK, Metro, and TVB’s JSG).

In 2007 Cheng changed labels and signed with Star Entertainment 星娛樂. She returned to the charts with “Big Girl” and “Tokyo Department Store”, earning five number-ones between the two singles. The album Super Girl was released on 19 September 2007. In 2008, she collaborated with Pakho Chau in the duet Nothing Accomplished 一事無成, and with MC Jin on “Useless Love Song”. Both these tracks were released in the album 23, released 30 October 2008. The album also contained the singles “Me Vs Me”, “Health Education”, and “Pay Back”. In 2009, Cheng released her first greatest hits album, Stephanie Cheng New + Best Collection, containing 25 tracks, including three new singles. Cheng for the most part of 2010 took a hiatus from music, only releasing a duet (愛得起) with Linda Chung and “Queen of Karaoke” K歌之后.

In 2011, Stephanie signed a management contract with Star Entertainment. She returned with the album Spring/Summer 2011 on 18 May 2011, with the intention of releasing a part two titled Fall/Winter 2011 containing dance tracks. Spring/Summer 2011 was supported by the release of “Kiss Kiss Kiss” and “Four Seasons” (written by Justin Lo), the former being a three-chart number one song. The album also featured songs composed by singers Ivana Wong, Pong Nan, and G.E.M.. In 2012, she released her second EP EVO which spawned the singles “The Fifth Kind”, “Gradually”, and “I Just Wanna Dance”. “The Fifth Kind” topped the RTHK and JSG charts.

On 4 June 2012 at a Metro Radio event, Cheng was interviewed by TVB host Shermaine Wong. Cheng was asked about her relationship with her boyfriend; she swore at Wong after the interview. This caused outrage with TVB and the interview was pulled from broadcast. Wong later interviewed Cheng again and showed to media Cheng’s apology on text message.

In 2014, Cheng signed a five-year deal with label Chessman Hong Kong. Her music at Chessman was noted by a deviation from her ballads, experimenting with electro and dance music.

In 2016, she returned to her first manager Starz People and signed with HMV Music, citing differences between her and Chessman. She co-headlined concert SS 2017 Live with singer-actress Shiga Lin at the Macpherson Stadium on 9–10 September 2017. In December 2017 she returned to the charts with the single “Unbreakable” 死不了的. The song reached number one on Ultimate 903 in 2018.