He joined Frederick Fung to work as a social worker in Sham Shui Po.

In 1986, he co-founded the Hong Kong Association for Democracy and People's Livelihood (ADPL) with Fung and other pro-democracy grassroots activists.

[1] In the 1995 Urban Council election, Tam won a seat in Sham Shui Po East uncontestedly.

In 2011 District Council elections, he was unexpectedly defeated by pro-Beijing independent Wai Hoi-ying in Nam Shan, Tai Hang Tung & Tai Hang Sai constituency when he tried to retain ADPL's seat from retiring party colleague Wong Kwai-wan.

[2] In 2016, Tam narrowly defeated chairwoman Rosanda Mok in a primary to stand again in Kowloon West for the 2016 Legislative Council election.