The son of an army major, Croker has little school education but does read widely while working in merchant trade. For some years Croker holds a position in the Admiralty, where his distant relative, John Wilson Croker, is his superior.
Croker devotes himself largely to the collection of ancient Irish poetry and Irish folklore. He assists in founding the Percy Society and the Camden Society. He and his wife’s testimonies about funereal customs, particularly the tradition of keening the deceased are among the earliest and most significant contributions to the understanding of the Irish language lament and the accompanying traditions. The first part of his Fairy Legends and Traditions of the South of Ireland is published in 1825. It grows to six editions and is translated into German by the Brothers Grimm (Irische Elfenmärchen, 1826). Parts two and three follow in 1828, the latter including Croker’s translation of the long Grimm preface to part one.
Croker publishes Legends of the Lakes: Or, Sayings and Doings at Killarney in 1829, in which he features discussions of the music of his friend, the Irish piper James Gandsey.