He was first elected as a candidate in the precinct of Wat Moha Leap from the Koh Sotin district in Kampong Cham Province in September 1955.
He was promoted as Secretary of State for Information and Religion in the second cabinet of the Sangkum from January 6 to 1 March 1956 under the presidency of Oum Chheang Sun.
[3] Trinh Hoanh is considered to have been instrumental in turning the National Assembly of Cambodia against Prince Sihanouk in a mounting crisis which led to the coup of 1970.
[4] Charles Meyer, the French senior adviser to the Prince, was aware of his influence and it came to no surprise to him when Chhang Song, who was to become Minister of Information in the Lon Nol-led Khmer Republic, heard these words from Trinh Hoanh at 2 p.m. on March 18, 1970: “I hereby withdraw my confidence from Samdech Head of State.” The National Assembly, in a unanimous decision, then voted to withdraw confidence from Prince Sihanouk and empowered House Speaker Cheng Heng as head of state.
[9] Under his watch, the main avenues in Phnom Penh were decorated with propaganda stating, “The Vietcong is worse than cholera.”[10] On 12 January 1974, Trinh Hoanh rejected the peace proposal of former Prime Minister Son Sann who suggested the departure of Lon Nol to restore national unity in Cambodia.
His assassination, if it may have been carried out for political reasons, made him the unfortunate forerunner of a tragic trend to exterminate all the intellectuals in Cambodia, which included anybody that would have worn glasses.