Lee, 41, grew up in a 300 sq ft flat on a public housing estate in Choi Hung with her parents and two siblings. After graduating in accountancy at the University of Science and Technology, she worked in a multinational firm and launched her political career at the age of 25.

She first stood for election in 1999, winning a seat on the Kowloon City District Council and becoming the youngest woman district councillor.

"As a young and new district councillor, Lee was very voluble and hard-working," says the Liberal Party's Ho Hin-ming, who has worked with Lee in the district council since then.

In 2003, still an independent, Lee was re-elected while the government-friendly camp suffered a huge setback after 500,000 people took to the streets to protest against government policies and plans to introduce controversial national security laws.

But a year later she was among a group of young professionals recruited by Tsang as the DAB aimed to broaden its reach to the middle class and professionals. The party was renamed the Democratic Alliance for the Betterment and Progress of Hong Kong after its merger with the Hong Kong Progressive Alliance in 2005.

Of her controversial decision to join the party at its darkest hour, she said then it had "seemed like a natural move".

"I have always believed that the city must forge a close partnership and trust with the mainland - before we can take action in areas such as democracy - because Hong Kong is part of China," she said in 2006.

Lee then contested a Legco election for the first time, ranking third on a DAB list in Kowloon West led by Tsang. Tsang won a seat but Lee fell short of the required number of votes. Yet despite this setback, her rise continued.

Felix Fong Wo, a founding member of the DAB and vice-chairman of the party's senate, recalls how he first got to know Lee in 2004 when she ran with Tsang.

"Tsang told me Starry was a young lady with good qualities. I also agreed she was presentable and had the potential to become a lawmaker in future," he says. "The majority of DAB members have a strong grass-roots image and obviously she is a different breed within the party."

In 2008 she took over from Tsang - who instead contested the Hong Kong Island constituency - to lead the party's team in the election and canvass the most votes in the constituency.

She also used her communication skills to raise her profile further. As many DAB lawmakers' command of English was weak, Lee would often speak on the party's behalf when responding to questions from the English media.

Like Lee, DAB lawmaker Gary Chan Hak-kan is one of the party's so-called younger generation who joined in the late 1990s.

"Lee is good at communicating with others and maintaining good relations with the younger as well as the older members of the party," Chan says. "Inside Legco, she is also widely accepted by colleagues from other parties. And so far, I have not heard anyone - even from rival parties - say anything bad about her.

Comparing Lee with another woman party leader, Emily Lau Wai-hing of the Democratic Party, Chan says: "Starry is gentle and speaks softly, never shouts. But don't mistake this for weakness. She is tough and can always put forward her views forcefully with good reasoning skills."

Lee's political career reached another level in 2012 when Chief Executive Leung Chun-ying appointed her to the Executive Council, the government's top decision-making body. Months later she won one of the five "super lawmaker" seats in the citywide constituency with 277,143 votes, ranking second.

However, her victory came at the expense of party colleague Lau Kong-wah - now the undersecretary for constitutional and mainland affairs - as she won more votes than expected in his New Territories stronghold.

Tam had initially planned to step down as chairman two years ago, but he decided to stay on when the succession plan did not go as smoothly as expected. Tam said at the time that the party's plan to groom talent had not worked out as successfully as it had hoped, and many core members had asked him to stay on for another two-year term.

Chris Ip Ngo-tung, DAB deputy secretary general, says Tam is a seasoned and sophisticated politician. "It is indeed a very bold step for him to step down as leader and give the job to the younger generation," Ip says.

"I look forward to her chairmanship. It is refreshing to have a woman lead the party," he says. "With a younger member as chairperson, it also shows the DAB has a good plan to rejuvenate the party and to set an example in Hong Kong of how a political party should grow."

Chan says Lee juggles her professional and private duties well. She is very close to her 12-year-old daughter and he recalls how she once called her to apologise for not being home for dinner because of Legco filibustering.

Lee's assistant of some years, Roger Kwan Ho-yeung, describes her as friendly and hard-working. "I don't have any doubts about her leadership,"

But a DAB core member, who spoke on condition of anonymity, says it will be difficult for Lee to rise to the same prominent status in the party as her predecessors, at least for now.

"When Jasper Tsang started to lead the party, he was also quite young, but the party has grown so much since then … So rather than relying on a few people, the party will move towards a more collective or team leadership, and to cooperate and supplement each other's strengths and weaknesses," he says.

Ivan Choy Chi-keung, a political scientist at Chinese University, says Lee might need a long time to build her authority in the pro-establishment camp, just as Tam did in the past.

"Tam has successfully led his party to contest previous elections and he took a leading role when there was joint action in the camp," says Choy.

"Other heavyweights in the bloc might also eye that leading role covetously. It remains to be seen whether Lee can take over from Tam to be the bloc's leader."