He edited William of Malmesbury's "De gestis regum anglorum" (2 vols., 1840); he continued and corrected John Le Neve's "Fasti ecclesiae Anglicanae" (3 vols., Oxford, 1854); and with Charles Trice Martin he edited and translated "L'Estorie des Engles" of Geoffrey Gaimar (1888–1889). He wrote "Syllabus in English of Documents in Rymer's Foedera" (3 vols., 1869–1885), and gave an account of the history of the public records from 1837 to 1851 in his "Memoirs of the Life of Henry, Lord Langdale" (1852). Hardy took part in the controversy about the date of the Athanasian Creed, writing "The Athanasian Creed in connection with the Utrecht Psalter" (1872); and "Further Report on the Utrecht Psalter" (1874).