Mechai Viradaidya founded the  Population and Community Development Association (PDA) in 1974 to address the unsustainable population growth rate in Thailand of over 3% annually at the time.  A variety of humorous, innovative, and unorthodox methods were utilized in conjunction with mobilizing and educating  a network of rural school teachers and  village community members to make contraceptives available throughout Thailand.  This resulted in the more sustainable population growth rate of 0.5% by 2003.  When HIV/AIDS first appeared in Thailand in the mid-1980s, similar methods were used to launch a major prevention program, which resulted in a 90% decline in new infections according to UNAIDS and  an estimated 7.7 million lives saved according to the World Bank, within 12 years.  In between running PDA’s activities, he was appointed to such key positions as Thailand’s Cabinet spokesman, the Minister of the Office of the Prime Minister, and Chairman of several  of Thailand’s largest government-owned enterprises.  He was also elected to the Senate between 1987-1991, 1996-2000, and 2000-2006.

Recognizing that civil society organizations cannot survive and expand solely on the generosity of others, Mechai Viravaidya established Thailand’s first social enterprise  to help fund the operating costs of PDA in 1975.  Since then, this company has spawned 18 other social enterprises which have contributed significantly to the financial needs of the association.  Perhaps the best known is the Cabbages & Condoms Restaurants and Resorts.

Following his success at promoting  contraception and HIV prevention,  Mechai has aggressively approached the problem of rural poverty by empowering the poor through the Village Development Partnership, to build sustainable entrepreneurial capacity, community empowerment for health, and income generating activities at the village level in Southeast Asia. This project is marked by extensive community involvement  as beneficiaries, planners, managers, and most importantly – as partners and leaders.  In 2010,  the VDP was expanded  from Thailand  into  Cambodia through assistance from the Bill & Melinda Gates Foundation.

In 2008, the Bamboo School was established by the Mechai Viravaidya Foundation to be a lifelong learning center for students as well as other citizens and a hub for social and economic advancement. This school strives to produce a new generation of honest, capable, and socially-conscious students who will perform at their full potential. The Bamboo School has also launched a new integrated rural development initiative to assist government primary schools in poor areas to also become a lifelong learning center and hub for social and economic progress in that area. This project is now known as the School-Based Integrated Rural Development program (School-BIRD).

For his efforts in various development  and educational  endeavors, Mechai Viravaidya has  been acclaimed with numerous awards, recognition, and  honorary doctoral degrees. These include the United Nations Population Award, the Bill and Melinda Gates Award for Global Health, the Prince Mahidol Award for Public Health, the Ramon Magsaysay Award for Public Service, and the Skoll Award for Social Entrepreneurship. He was also named one of Asiaweek’s “20 Great Asians”, and one of TIME Magazine’s “Asian Heroes” to mark the magazine's 60th year of its publication in Asia.