Martyn Day (born 26 March 1971) is a Scottish National Party (SNP) politician, who served as the Member of Parliament (MP) for Linlithgow and East Falkirk from 2015 until 2024.

After the 2012 Scottish local elections, the SNP found themselves in opposition in West Lothian and Day took on the post of spokesperson for Development and Transport and group whip.

Day was selected to contest the Linlithgow and East Falkirk constituency at the 2015 general election, when he defeated the sitting Labour MP, Michael Connarty.

At the 2019 general election, Day was re-elected again, with an increased majority of 11,266 votes, with Charles Kennedy of the Conservatives finishing in second place.

He was defeated by Kirsteen Sullivan of Scottish Labour, losing by a majority of 8,323, and finished in second place.