Legislative Council career
In the 2008 Legislative Council election, Tsang switched his constituency to Hong Kong Island, allowing Lee to stand for the vacant seat he left in Kowloon West. Her campaign was run by Kan Chi-ho, who was also Tsang's campaign manager. Kan took Lee to meet community leaders to seek their support. She was ranked first on the candidate list, before Chung Kong-mo, Chan Wai-ming, and Vincent Cheng.
Lee's list received 39,013 votes (18.9%), the most in the constituency, allowing her to join the Legislative Council. As a new legislator, she was unfamiliar with many public policy issues and found it difficult understand them in a short period of time.
In 2011, she was elected vice-chairwoman of the party.
In 2012, she was appointed to the Executive Council by Chief Executive Leung Chun-ying. At the time, she was the only person to hold positions in three different levels of representative councils, the Executive, Legislative and District Councils. She served on the Executive Council until her resignation in March 2016 to focus on her work on the Legislative Council and the party. Her position was taken by Ip Kwok-him, a long-time DAB legislator.
In the 2012 Legislative Council election, Lee left Kowloon West to contest one of five seats in the new District Council (Second) functional constituency that is elected by all voters in Hong Kong. Her ticket received 277,143 votes (17.4%), the second-most votes received behind the ticket of the Democratic Party's James To that received 316,468 votes (19.9%).
On 17 April 2015, she replaced Tam Yiu-chung as the leader of the DAB, making her the first woman to hold the post. She was the youngest party chairperson at age 41; the transition was described as a generational shift. DAB legislator Leung Che-cheung commented that Lee was qualified but inexperienced to assert authority, unlike veteran politicians such as Tam or Ip Kwok-him. Lee said that the party did not operate by personal authority but consultation and discussion.
On becoming leader, Lee said she aimed to take more seats in the 2015 District Council elections by focusing on voters who were against the 2014 Hong Kong protests, and to continue to support universal suffrage in Chief Executive elections from 2017.
In March 2016, she resigned from the Executive Council to focus on the DAB.
After Lee was re-elected in the 2016 election, she succeeded Andrew Leung of the Business and Professionals Alliance for Hong Kong (BPA) as the House Committee chairperson, the second-highest office in the Legislative Council.
On 18 May 2020, Lee was re-elected as House Committee chairperson. Prior to the vote, Chan Kin-por, the nominee of Legislative Council president Andrew Leung, had taken the seat of the presiding member – a position which had been held since October 2019 by pro-democrat Dennis Kwok – with the help of security personnel, and 15 pro-democratic lawmakers had been removed from the meeting room after scuffles had broken out; during Lee's election, three pro-democrats sat outside the room in protest. After the physical removal of the pro-democratic lawmakers, Lee was elected.
In March 2021, Lee supported changes that would reduce the power of Legislative Council members, claiming that opposition members had blocked legislation and caused a power vacuum.
In October 2021, Lee and fellow lawmaker Holden Chow were criticised by the mother of Amber Poon, claiming that Lee and Chow were "vanishing" after holding a press conference in 2019 with her, to push forward the 2019 Hong Kong extradition bill.
During the 2021 Hong Kong legislative election, Lee dismissed concerns that the record-low voter turnout of 30.2% was problematic.
In December 2021, Lee was re-elected through Kowloon Central constituency with 95,976 votes.
In January 2022, Lee, Andrew Leung and Ma Fung-kwok pushed for the Chinese national emblem to be permanently added to the Legislative Council chamber. Leung had earlier said it would be only temporary for the swearing in of lawmakers.
In August, Lee announced that 16 members of the DAB would travel overseas to clarify any "misunderstandings" businesspeople may have about Hong Kong.
In November, after a rugby match in South Korea played Glory to Hong Kong for the Hong Kong team, Lee said that Asia Rugby should apologise to "the entire [Chinese] population."
