After becoming ordained in 1804, he first labored in Ireland until moving to London around 1810. In 1835, Lord Brougham, a Whig patron and relative, helped Croly become Rector of St Stephen Walbrook, in the slums. It was there he opened a pulpit that had been closed for a hundred years and developed a high reputation as a preacher. He also served at the same time in St Benet Sherehog. He retained both positions until his death.

He wrote poems, dramas, satires, novels, history, and theological works, and attained some measure of success in all. Perhaps his best known works are his novels, Salathiel (1828), founded on the legend of the Wandering Jew, and Mareton (1846). He wrote as a dramatic critic to the New Times and later as a foreign correspondent. Croly was the leading contributor to the Literary Gazette and Blackwood's Magazine, published from 1817—25. Croly was also associated with the Tory magazine Britannia. His chief contribution to theological literature is an exposition of the Apocalypse. One of his hymns is Spirit of God, descend upon my heart written in 1854.