Madden was largely self-educated. In 1826, he was appointed to the staff of the British Museum, and subsequently became keeper of MSS from 1837 to 1866. Madden did much to establish scholarly editorial standards for medieval English texts and produced (among others) the first editions of Havelok the Dane (1828), William and the Werewolf (1832), and Sir Gawain and the Green Knight (1839). He also wrote widely on many aspects of medieval literature, history, palaeography, and MS studies. His extensive and valuable diary is held in the Bodleian Library.
From The Oxford Companion to the Book in Oxford Reference.