Plouguenast-Langast (; ) is a commune in the Côtes-d'Armor department of Brittany in northwestern France. It was established on 1 January 2019 by merger of the former communes of Plouguenast (the seat) and Langast.
Plouguenast-Langast has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Plouguenast-Langast is . The average annual rainfall is with January as the wettest month. The temperatures are highest on average in August, at around , and lowest in January, at around . The highest temperature ever recorded in Plouguenast-Langast was on 9 August 2003; the coldest temperature ever recorded was on 2 January 1997.
Population data refer to the commune in its geography as of January 2025.