Lee is famous for, amongst others, playing the title role in Singapore's Mediacorp Channel 5 television sitcom Police & Thief as Lee Tok Kong, Phua Chu Kang Pte Ltd as guest appearance Lee Kok Peng from season 5 until season 7 and in Mediacorp Channel 8 long series television drama Holland V as Su Hao. He also gained recognition for his work with Jack Neo and Henry Thia in films such as Money No Enough and Liang Po Po: The Movie and long-running comedy variety programme Comedy Nite (搞笑行动). He made his directorial debut in the comedy horror film The Ghosts Must Be Crazy.

Along with long-time colleague Christopher Lee, Mark Lee was awarded the coveted All Time Favourite Artiste award in the Star Awards 2010 and became the first host-cum-comedian to win the award as the previous winners were predominantly thespians. As such he will no longer be in the run for the Top 10 Most Popular Male Artistes awards in future Star Awards.

Although Lee was mostly known for playing comedic roles early in his career, he has also diversified into hosting and hosted various kinds of programmes, mainly infotainment, travelogue and DIY programmes. He co-hosted the popular home makeover programme Home Decor Survivor and the infotainment programme Behind Every Job with Bryan Wong, which won both a string of nominations in the hosting categories at the Star Awards. In 2012 he won his fourth Best Variety Host award for his popular show It's a Small World (season 2).

Lee was always given an on-screen name/surname of Ong or Huang, particularly in Jack Neo's movies, with the exception of Liang Po Po: The Movie, That One Not Enough and Ah Long Pte Ltd.

On 9 March 2017, Lee opened a production house King Kong Media Production with partner Yinson Marine Services, a Malaysian oil and gas company. He is now working on a film project for 2018.