Along with fellow North Eastern MPs elected in 2010, Ian Lavery and Grahame Morris, Mearns is perceived to be on the left-wing of the Labour party.

[8] He was one of 16 signatories of an open letter to Ed Miliband in January 2015 calling on the party to commit to oppose further austerity, take rail franchises back into public ownership and strengthen collective bargaining arrangements.

[10] He was a member of the bill committee for HS2, which he has criticised for treating residents of the north east and other regions not served by the line as "lesser citizens".

[11] In March 2013, Mearns resigned as PPS to Ivan Lewis to defy the Labour whip and vote against the Jobseekers (Back to Work Schemes) Bill which retroactively changed DWP rules relating to Workfare in the United Kingdom.

[13] On 24 February 2022, following the 2022 Russian invasion of Ukraine, Mearns was one of 11 Labour MPs threatened with losing the party whip after they signed a statement by the Stop the War Coalition which questioned the legitimacy of NATO and accused the military alliance of "eastward expansion".