'propopulationist' originates from modern English, specifically a compound formed from the prefix 'pro-' (from Latin 'pro' meaning 'for'), the noun 'population' (from Latin 'populatio' / 'populus' meaning 'people'), and the agentive suffix '-ist' (via Greek/Latin/Old French meaning 'one who advocates or practices').

'population' entered English via Latin 'populatio' and Old French; the prefix 'pro-' (Latin) has long been used in English to mean 'in favor of' and the suffix '-ist' was attached to form agent nouns. The modern coinage 'propopulationist' is a recent English compound combining these elements.

Initially the components meant 'for' + 'people' + 'advocate/practitioner'; over time the compound came to mean specifically 'an advocate of increasing population' (supporter of population growth or pronatalist policies).