He is one of the four regular hosts of the podcast No Such Thing as a Fish, together with Dan Schreiber, Andrew Hunter Murray, and Anna Ptaszynski.

[5] After graduating, he took a job as an accountant in Salford[6] and Eccles,[7] working first at a chain of hotels and then for a hospitality company.

[9][10] In March 2014 QI launched the spinoff podcast No Such Thing as a Fish, with Harkin as one of the show's four regular hosts.

[7][17] Harkin's education in mathematics and physics, and his background in accounting, mean that he often supplies numerical or natural science facts for QI and No Such Thing as a Fish,[9] and his use of puns has been reviewed positively.

[18] In July 2024, Harkin and Anna Ptaszynski released the first episode of their new podcast Quite a Good Sport.