Mechai Viravaidya founded the non-governmental organization, Population & 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 communities to make contraceptives available throughout Thailand. This resulted in the more sustainable population growth rate of 0.5% by 2005. When HIV/AIDS first appeared in Thailand in the late 1980s, similar methods to promote safe sex and prevent the disease were implemented, which resulted in an estimated 7.7 million lives saved according to a 2005 World Bank study.

Following his success at promoting contraception, Mechai Viravaidya began poverty eradication programs to provide access to credit and business skills training to rural villagers in Thailand. This program eventually became known as the Village Development Partnership (VDP) program and is a comprehensive approach that focuses on community empowerment, income generation, environmental promotion, health, and education. The VDP model was employed in the south of Thailand for communities devastated by the Tsunami in 2004, and in the last 22 years, Mechai and his team have worked in over 400 villages throughout Thailand. In 2010, the VDP was expanded into Siem Reap Province, Cambodia through funding from the Bill & Melinda Gates Foundation.

Understanding the importance of education to create the next generation of philanthropists and good citizens, Mechai established the Mechai Viravaidya Foundation and opened the Mechai Pattana School in Northeastern Thailand in 2009.