MacCarthy was born in Lower O'Connell Street, Dublin, on 26 May 1817,[1] and educated there and at St Patrick's College, Maynooth.

[2] He acquired an intimate knowledge of Spanish from a learned priest, who had spent much time in Spain, which he was later to turn to good advantage.

In the same year he edited The Poets and Dramatists of Ireland, which he prefaced with an essay on the early history and religion of his countrymen.

The delicate health of some members of his family then rendered a change of climate imperative, and he paid a prolonged visit to continental Europe.

On his return MacCarthy settled in London, where he published – in addition to his translations – Shelley's Early Life, which contains an account of that poet's visit to Dublin in 1812.

His success is sufficiently testified by George Ticknor, who declared in his History of Spanish Literature that MacCarthy "has succeeded in giving a faithful idea of what is grandest and most effective in [Calderon's] genius... to a degree which I had previously thought impossible.