'matrimonialist' originates from Modern English, specifically formed from the adjective 'matrimonial' plus the agent suffix '-ist' meaning 'one who advocates or practices'.

'matrimonial' in turn originates from Latin 'matrimonium' meaning 'marriage', where the element 'matri-' is related to 'mater' meaning 'mother' and the suffix '-monium' denoted a state or condition; 'matrimonium' entered English via Old French/Medieval Latin influences and became 'matrimonial' in Modern English, and later compounds such as 'matrimonialist' were formed.

Initially, the root term meant 'marriage' (the state of being a mother or a married state), but over time derivatives like 'matrimonial' came to mean 'relating to marriage', and 'matrimonialist' took on the narrower sense of 'one who advocates for or specializes in matters of marriage'.