He is the founding member of the largest pro-Beijing party the Democratic Alliance for the Betterment and Progress of Hong Kong (DAB) from 1992 to 2003 and the 2nd President of the Legislative Council from 2008 to 2016.

Graduated from the University of Hong Kong, Tsang chose to teach in the leftist Pui Kiu Middle School and became its principal before he stepped into politics in the 1980s.

In 1992 he founded the Democratic Alliance for the Betterment of Hong Kong and first contested in the 1995 Legislative Council election in which he lost the race.

Tsang received his primary and secondary education at St. Paul's College run by the Hong Kong Anglican Church.

Tsang grew his patriotic sentiments and interest in Marxism by reading the leftist newspaper Wen Wei Po which his father brought home from work everyday and worshipped Qian Xuesen, a renowned scientist who returned to the mainland from the United States in the 1950s.

He proclaimed himself a Marxist and studied works of Karl Marx and Mao Zedong with like-minded classmates at a time when the majority of the students at the University of Hong Kong supported the colonial rule and had negative views on the Chinese Communist Party (CCP).

[1] He joined several university students in making donations to the leftist unions through Wen Wei Po following the industrial dispute at the Hong Kong Artificial Flower Works in April 1967 which later escalated to large-scale riots.

In the wake of his brother's event, Tsang gave up the plans to further his studies abroad although he had been accepted by four prominent universities in the United States.

In the 1995 Legislative Council election, he ran in Kowloon Central but was defeated by the less known candidate Liu Sing-lee from the pro-democracy Association for Democracy and People's Livelihood (ADPL).

During the controversy surrounding the enactment of the national security bill in Hong Kong, Tsang drew criticism for his party's support of the government's legislative initiatives.

Tsang was also criticised for the manner in which he presided over Legislative Council meetings, which led to walkout protests, though he was generally perceived to be fair and accommodating and enjoyed friendly relations with both pro-Beijing and pan-democratic members.

"[9] In the run-up to the 2012 Chief Executive election, he was noted for his relatively liberal views on issues such as universal suffrage,[10][11] and initially expressed interest in putting himself forward as a candidate, before later backing out.

The pan-democrats questioned Tsang's neutrality in the chamber, seeing the text messages as "clear evidence" that he was colluding with the rest of the government's allies and planned to mull a no-confidence vote against him.

[13] On 1 July 2015, Tsang was awarded the Grand Bauhinia Medal, the SAR's highest honour, in recognition of his public service, particularly his presidency of the Legislative Council.