McNulty was born on 14 December 1982 in Hanover, Lower Saxony, West Germany,[1] and lived in Berlin and Münster,[1] before moving to Atherton, Greater Manchester, England,[1] when he was 10 years old.

[1] He attended Hesketh Fletcher high school, Atherton,[1] then furthered his education at Winstanley College in Wigan.

[1] At 15 years of age, he was a lead in a school play, and enjoyed the role enough to make acting a career choice.

[1] McNulty was attending drama classes in Manchester when casting director Judi Hayfield approached him to audition for his first feature film.

[3] In 2006, he played his first lead role in See No Evil: The Moors Murders,[1] alongside Joanne Froggatt, Sean Harris, and Maxine Peake.