 Armstrong played drug dealer-turned-kidnapper Ashley Cowgill in Sally Wainwright's 2014 crime drama "Happy Valley", starring Sarah Lancashire.In December 2016 he also appeared as William Allison in Wainwright's "To Walk Invisible", a television biopic about the lives of the Bronte family.In 2016, he appeared in "Hated in the Nation", an episode of the anthology series "Black Mirror".