As of the last official census in 2011, Namchi had a municipal population of 12,194, though estimates suggest the current population exceeds 15,000 due to rapid urbanization and rural-to-urban migration.
The demographic fabric of Namchi is highly diverse and harmonious. The majority of the population comprises ethnic Indian Gorkhas (Nepalis), alongside significant communities of Bhutias, Lepchas, and internal migrants from other Indian states who have settled for business and government work.
Hinduism and Buddhism are the dominant religions, vividly reflected in the city's monumental architecture and daily life. Christianity also has a meaningful presence. Nepali is the lingua franca, while English is widely spoken and serves as the primary language for administration and higher education. Hindi is also broadly understood and spoken, especially within the tourism sector.