Martyn was appointed as Deputy Leader of Bolton Council (the only Conservative-led Council in Greater Manchester) and Executive Cabinet Member in May 2019. He is responsible for skills, development and regeneration and economic issues, as well as town centres - including the town centre strategy, sports, tourism, libraries, museums and cultural services strategies, special projects, land and property. 

He was first elected to Bolton Council in 2003 and has been a Councillor for Westhoughton North and Chew Moor since 2010. He was re-elected for the 5th time in May 2018.