He is Professor Emeritus at the UP Film Institute of the College of Mass Communication (CMC), University of the Philippines Diliman. He served as dean of the CMC, 2003-2006;  vice president and artistic director of the Cultural Center of the Philippines, 1986-1994; and   chair of the MTRCB, 2001. He was founding member and former chair of the Manunuri ng Pelikulang Pilipino. He published  pioneering books on Philippine theatre forms, like the komedya, sinakulo and sarsuwela, as well as publications on the Filipino cinema, like the four  volumes of The Urian Anthology covering the history of the Filipino cinema from 1970 to 2009, and The Cinema of Manuel Conde.   He edited and published the 10-volume CCP Encyclopedia of Philippine Art and the 30-part Tuklas Sining monographs and videos on the Philippine arts. He has written full-length plays as well as scripts for documentaries on Philippine theatre, costumes, and festivals. 

Tiongson was a Visiting Professor at Osaka University of Foreign Studies in Japan; and Fulbright Visiting Professor at the University of California, Berkeley; University of Michigan; University of California, Los Angeles; and University of Hawaii at Manoa. Tiongson also received an Australian Cultural Award for his extensive research on Philippine culture, resulting in two pioneering works on Philippine drama: Kasaysayan at Estetika ng Sinakulo at Ibang Dulang Panrelihiyon sa Malolos and Kasaysayan ng Komedya sa Pilipinas.

Tiongson was vice-president and artistic director of the Cultural Center of the Philippines (CCP) from 1986 to 1994. He conceptualized a new direction for the CCP, in 1986, and subsequently authored a comprehensive cultural development plan that has broadened the scope of the CCP Outreach Programs nationwide. He paved the way to give more opportunities and recognition for regional artists and arts organizations through productions, conferences, forum-lectures, publication and research. He continuously writes history and criticisms about local arts and culture that serve as reference materials of scholars, researchers, academicians, and young students of the present generation.

Tiongson was also the Philippine Director of Sangandaan 2003, a cultural commemoration that highlighted the arts and media produced by Filipinos, Americans and Filipino-Americans in the course of Philippine-U.S. relations from 1899 to 2002. The cultural events were commemorated in the Philippines on July 6–30, 2003 under the sponsorship of the University of the Philippines, the Cultural Center of the Philippines and the San Francisco State University, in collaboration with numerous public and private institutions in the Philippines such as the National Commission for Culture and the Arts, the National Historical Institute, the National Library, the National Museum, the Metropolitan Museum of Manila, Ateneo de Manila University, and De La Salle University-Manila, and in the United States such as the City College of San Francisco, and the University of San Francisco.

Tiongson has taught Philippine literature, theater, and general culture at the University of the Philippines, the Ateneo de Manila University, De La Salle University-Manila, the University of Hawaii and the Osaka University of Foreign Studies. He also taught Filipino and Philippine literature at the College of Arts and Letters, University of the Philippines from 1974 to 1986. Among the books he edited are: The Cultural Traditional Media of ASEAN, The Urian Anthology, the Politics of Culture: The Philippine Experience, Tuklas Sining, and the 10-volume CCP Encyclopedia of Philippine Art. For his publications, he has received five National Book Awards from the Manila Critics Circle and two Surian ng Wikang Pambansa awards.

In 2014, he wrote and produced the musical docudrama, Ang Kababaihan ng Malolos / The Women of Malolos, based on his book The Women of Malolos.