Melgven (; ) is a commune in the Finistère department of Brittany in northwestern France.
Melgven has an oceanic climate (Köppen climate classification Cfb). The average annual temperature in Melgven is . The average annual rainfall is with December as the wettest month. The temperatures are highest on average in July, at around , and lowest in January, at around . The highest temperature ever recorded in Melgven was on 9 August 2003; the coldest temperature ever recorded was on 17 January 1985.
Inhabitants of Melgven are called Melgvinois in French.