In an election which saw the SNP gain 56 seats, Day was amongst a number of MPs who overturned previous Labour Party majorities. Day defeated Michael Connarty the Labour Party MP who held this seat from 2005 to 2015. 
Following the announcement of a moratorium on fracking in Scotland in September 2016, Day said he would oppose fracking irrespective of whether research could prove the industry was safe, saying:
- 'Fracking is something I don't want to see happen. Even if they come back with evidence to say this can be done, technically, safely and without a problem, the issue then becomes reputational damage. This modern technology - fracking - frightens people and they're not convinced by it.' 
He is a member of the All-Party Parliamentary Group on Shale Gas Regulation and Planning.
- Christina Johnston - Assistant registrar, West Lothian Council
- Iain Sinclair
- Callum Timms
- Andrea Zorzetto 
- Martyn Day Express, accessed 12 May 2015
- Election 2015: Nicola Sturgeon declares SNP tidal wave a 'historic watershed' as Labour is wiped off political map in Scotland The Daily Record, 8 May 2015, accessed 12 May 2015
- Daniel Sanderson, SNP MP: I'll fight fracking in Scotland even if it research commissioned by Nicola Sturgeon proves it's safe, The Herald, 27 September 2016, accessed 20 December 2016.
- Register of interests of members' secretaries and research assistants, 23 March 2016, parliament.uk, accessed 19 April 2016