Kelly grew up among the Dublin working class and they, along with the petty bourgeoisie and lower intelligentsia, make up the bulk of the characters in his works.
His best-known works are the novel Strumpet City, set in Dublin in the years leading up to the lockout of 1913 and during the course of the strike, and the short stories in the collection The Trusting and the Maimed.
During the 1960s, Plunkett worked as a producer at Telefís Éireann.
He won two Jacob's Awards, in 1965 and 1969, for his TV productions.
In 1971 he wrote and presented "Inis Fail - Isle of Destiny", his very personal appreciation of Ireland.