Merioneth, sometimes called Merionethshire, was a constituency in North Wales established in 1542, which returned one Member of Parliament (MP) to the House of Commons of the English Parliament, and later to the Parliament of Great Britain and of the United Kingdom. It was abolished for the 1983 general election, when it was largely replaced by the new constituency of Meirionnydd Nant Conwy.

Until 1974, Merionethshire or Merioneth was an administrative county in the north-west of Wales, later classed as one of the thirteen historic counties of Wales.