'MP' originates from English, specifically the phrase 'Member of Parliament', where 'Member' meant 'one who belongs to or is part of' and 'Parliament' comes from Old French 'parlement' meaning 'a speaking or discussion'.

'MP' developed as an initialism/abbreviation of the phrase 'Member of Parliament' in written records and informal speech; the phrase 'Member of Parliament' itself comes from Middle English usage of 'member' + Old French 'parlement'.

Initially it referred primarily to a person elected to the UK Parliament; over time the initialism has been used for members of similar legislatures in other countries and has also been adopted as an abbreviation for other terms (e.g., 'military police', 'megapixel').