Before the Act of Union 1707, the barons of the sheriffdom or shire of Berwick (also called the Merse) elected commissioners to represent them in the unicameral Parliament of Scotland and in the Convention of Estates. The number of commissioners was increased from two to four in 1690.
During the Commonwealth of England, Scotland and Ireland the sheriffdom was represented by one Member of Parliament in the Protectorate Parliament at Westminster. After 1708, Berwickshire returned one member to the House of Commons of Great Britain and later to the House of Commons of the United Kingdom.