He completed his secondary (1982) and matriculation (1984) studies at Salesian High School. At that time, he was already actively involved in the school debating team, speech and inter-school quiz competitions.

He was already interested in politics when he studied Business Management at the Chinese University of Hong Kong. He was the Vice-President of the Student Union of the Chinese University of Hong Kong in 1986 and the President of the Student Union in 1987, and actively took subjects from the Department of Politics and Administration.

After completing his Bachelor's Degree, he specialized in Politics at the Graduate School of CUHK and began to focus his research on electoral systems. After completing his master's program, he taught at the University of Macau and the City University of Hong Kong. In 2004, he became a senior tutor in the Department of Political Science and Administration at the Chinese University of Hong Kong.

In addition to his academic writings, he has been an active commentator in the press, radio and television, and has been a host of radio political programs for many times. Between May and August 2004, he was the temporary host of "Teacups in the Storm" on Commercial Radio Hong Kong, and was involved in the "Celebrities Banning Incident" which caused quite a shock at that time. He was involved in the "Celebrity Talk Show" incident, which caused quite a shock at the time. He also ceased hosting the program "Tea Cup in the Storm" for Commercial Radio after the dismissal of the former Chief Operating Officer, Mr. Choi Tung-ho, who had been appointed as the Vice Chairman of the Board of Directors of Commercial Radio by Hang Seng. He recently hosted the RTHK Television Division's reading program "Reading Decoded", which aired between April and June 2008, together with Wong Nim-yan.

To this day, he has been actively involved in Hong Kong's pro-democracy movement, along with young scholars such as Chan Kin Man, Ma Ngok and Lee Wing Yee, and is a member of the organization that promotes universal suffrage, the Network for the Development of Democracy (NDD).

Tsoi Tze-keung is popular with students at the Chinese University of Hong Kong, where he is known as Professor Egghead. The name originates from his resemblance to Dr. Egghead, the angular Dr. Egghead in the Supermouse.