'pro-lifer' originates from English, specifically the compound 'pro-life' plus the agentive suffix '-er', where 'pro-' meant 'in favor of' and 'life' meant 'life'.

'pro-lifer' developed in the 20th century by adding the agentive suffix '-er' to the political phrase 'pro-life' (formed from 'pro-' + 'life') to denote a person holding that position; it arose during public debates over abortion.

Initially it referred specifically to a supporter of the 'pro-life' movement; over time it has remained largely the same but has taken on political and activist connotations in public discourse.