[4] Joining the Samahang Demokratiko ng Kabataan (Association of Democratic Youth; SDK) as a student, he would eventually become a member of the CPP, in which he helped organize labor unions in Marikina and Caloocan.

Tiamzon secretly married his fellow activist Wilma Austria in early 1973, but was later arrested and detained in Fort Bonifacio by July during martial law.

A boat explosion off the coast of Samar during an AFP Joint Task Force operation on August 22, 2022, is speculated to have resulted in the deaths of Tiamzon and Wilma,[6] but the military refrained from confirming this due to lack of evidence.

[1] Tiamzon recalled in an interview with Bulatlat that his efforts for the Leftist movement began when he attended his first demonstration on January 26, 1970 during the State of the Nation Address of President Ferdinand Marcos, which marked the beginning of the First Quarter Storm.

Tiamzon along with his spouse, a fellow senior member of the CPP leadership, and five other persons were arrested by Philippine security forces in Cebu in 2014 during the presidency of Benigno Aquino III; they had been exposed by surveillance since relief operations began in the wake of Typhoon Haiyan the year before.

The Tiamzons were wanted on murder charges as a consequence for their alleged involvement in the deaths of fifteen civilians whose remains were discovered in a mass grave in Inopacan, Leyte in 2006.

[3] They were released from detention in August 2016 upon the order of President Rodrigo Duterte as they were designated representatives of the National Democratic Front to the peace talks with the Government of the Philippines to be held in Oslo, Norway.

[14] Duterte announced that peace negotiations would no longer be undertaken in February 2017 and that he expected the NDF representatives, including the Tiamzons to "on their own… return and go back to prison.

The previously reported mid-sea firefight and explosion, which were believed to have caused their deaths, were, according to the CPP, a cover-up by the AFP and its US military advisers for their "fascist crime".