When it became clear his future did not lie in professional football, Waddell turned to his other love and began to write (he would later combine the two in the Napper series of football-centred children's books).
Originally, he wrote for adults; his first real success was a comic thriller, Otley, which was made into a film starring Tom Courtenay and Romy Schneider.
After moving back to Northern Ireland in the late 1960s, he wrote books that reflected on the changing situation in his native land.
Waddell and Firth won the Kurt Maschler Award, AKA the Emil, for The Park in the Dark (Walker, 1989).
From 1982 to 1999, the award annually recognised one British "work of imagination for children, in which text and illustration are integrated so that each enhances and balances the other.