'campaign' originates from French, specifically the word 'campagne', where the element 'camp-' (from Latin 'campus') meant 'field' and referred to open country or military ground. 'Campaigner' is formed in English by adding the agent suffix '-er' to 'campaign'.

'campaign' changed from Old French 'campagne' and Medieval Latin influences into Middle English forms such as 'campaigne', and eventually became the modern English word 'campaign'. The agent form 'campaigner' developed later in English by suffixation ('campaign' + '-er').

Initially, 'campaign' often referred to military operations or activity in the field ('a series of military operations'); over time it broadened to mean any organized series of actions to achieve a goal, and 'campaigner' came to mean 'a person who takes part in or leads such organized efforts'.