He is credited with modernising the nation's capital Phnom Penh and designing several iconic landmarks, including the Independence Monument, Chaktomuk Conference Hall and Olympic Stadium.

[3][2] After being the first student to pass the Bacc II at Preah Sisowath High School in 1944,[4] Molyvann obtained a scholarship to pursue studies in Paris, France, in 1946.

Molyvann returned to Cambodia in 1956 during its Sangkum Reastr Niyum era as one of only a handful of trained Cambodian architects, whom Prince Norodom Sihanouk called on to lead the design of new state infrastructure.

[3][8][9] During this post-independence era, Molyvann designed and built over 100 structures, including many famous landmarks, such as Chaktomuk Conference Hall, the Council of Ministers and the State Palace in the capital.

[9] Built in less than two years with the intent for it to house the 1963 Southeast Asian Peninsular Games that were then awarded to Indonesia, it was only inaugurated in 1964, and became known as the Olympic Stadium.

[3] It hosted such important events as the GANEFO games[6] and the President of France, Charles de Gaulle's state visit, in 1966.

[13] Impressed with his work in Phnom Penh, Lee Kuan Yew offered Molyvann the opportunity to help design a new Singapore, which he declined.

Molyvann had been the Sangkum's longest serving Minister of Education[14] and was a likely target to reprisals from the new regime due to his close relationship with Sihanouk.

[15][6] During the Khmer Rouge era, many of his buildings were abandoned or used as imprisonment or execution sites after Phnom Penh was forcibly evacuated.

[16] The Khmer Rouge unsuccessfully attempted to destroy the National Bank in Sihanoukville, and used the Sports Complex for mass rallies.

[5] Later in life, Molyvann expressed resentment that modern urban development in Phnom Penh was failing to consider its environment and water management, creating greater risk of flooding.

[9] The National Sports Complex was sold to a private developer in 2001 which filled up its vital hydraulic system, consisting of moats and water treatment stations, with shoddy constructions, hence compromising its survival and increasing flood risk.

[4] His funeral was held on 1 October 2017 in Siem Reap, with some of his ashes released into the water to the east of Angkor Wat before dawn, and others beside a stupa that Molyvann had designed.

[19] His work in modernising Phnom Penh whilst incorporating traditional designs and the local environmental conditions led to him being nicknamed "the man who built Cambodia".

[8] Molyvann's 100 Houses remained a residential area at the time of his death, despite limited conservation work taking place on the buildings.