Maidment's hobby was the collection of literary rarities. He edited and published editions of ancient literary remains including A Book of Scottish Pasquils, 1568-1715, a selection from the papers of the family of Boyd of Kilmarnock from the 16th and 17th centuries, state papers and miscellaneous correspondence of Thomas, Baron Melros (from the 17th century), letters and state papers during the reign of King James the Sixth, chiefly from the manuscript collections of Sir James Balfour of Denmylne, constitutions, charters etc. of the nunnery of Sciennes, 1512–88, and Scottish Ballads and Songs: Historical and Traditionary.
He was born in London about 1795; his father was a solicitor. Called to the Scottish bar in 1817, he soon took a high position as an advocate in cases involving genealogical inquiry, and was much involved in disputed peerage cases. He died in Edinburgh, 24 October 1879, and was buried in the Dean cemetery. He was an extensive collector, and the sale, in May 1880, of his library occupied fifteen days.
Maidment showed an early taste for antiquarian and historical research, and he became friends with Sir Walter Scott, Charles Kirkpatrick Sharpe, and other men of letters. His publications were very numerous, though many were anonymous, and several were privately printed in small editions. He published generally with John Stevenson and his son Thomas George Stevenson. He edited works for the Bannatyne, Maitland, Abbotsford, and Hunterian Clubs, and for the Spottiswoode Society; and he was the main editor of John Kay's Edinburgh Portraits, 2 vols. 1837. One of his major works is the Dramatists of the Restoration,’ 14 vols. Edinburgh, 1877, in the editorship of which he was assisted by William Hugh Logan.
Other of Maidment's compilations were:
- Nugæ Derelictæ: Documents illustrative of Scotish Affairs, 1206–1715, with Robert Pitcairn, 1822.
- Reliquiæ Scoticæ: Scotish Remains in Prose and Verse, from Original MSS. and Scarce Tracts, 1828.
- Letters from Bishop Percy, John Callander of Craigforth, David Herd, and others, to George Paton (late of the Custom House, Edinburgh), with an Appendix of Illustrative Matter, Biographical Notices, &c., 1830.
- Historical Fragments relative to Scotish Affairs from 1635 to 1664, 1832–3.
- The Argyle Papers, from the manuscripts of Robert Mylne, 1834.
- Galations: an Ancient Mystery, 1835, taken down from the recitations of the Guisards at Stirling about 1815.
- Fragmenta Scoto-Dramatica, 1715–1758, from Original Manuscripts and other Sources, 1835.
- Bannatyniana: Notices relative to the Bannatyne Club, instituted in February M.DCCC.XXIII.; including Critiques on some of its Publications; with a curious Prefatory Notice, including Letters to and from Sir Walter Scott, Notes, &c., 1836.
- Analecta Scotica: Collections illustrative of the Civil, Ecclesiastical, and Literary History of Scotland, chiefly from Original Manuscripts, 2 vols. 1834–7.
- Roxburgh Revels, and other relative Papers; including Answers to the Attack on the Memory of the late Joseph Haslewood, with Specimens of his Literary Productions, 1837.
- Court of Session Garland: with an Appendix, 1839.
- Scotish Elegiac Verses on the Principal Nobility and Gentry, from 1629 to 1729, with interesting Biographical Notices, Notes, and an Appendix of illustrative Papers, 1842.
- The Spottiswoode Miscellany: a Collection of Original Papers and Tracts, illustrative chiefly of the Civil and Ecclesiastical History of Scotland, with Biographical Notices and Notes, 2 vols. 1844–5.
- Genealogical Fragments, 1855.
- Scotish Ballads and Songs, with illustrative Notes, &c., 1859.
- A Book of Scotish Pasquils, 1568–1715, edited with Introductory and Prefatory Remarks, 1868.
- A Packet of Pestilent Pasquils, a supplement to the Book of Scotish Pasquils, privately printed, 1868.
His publisher, Thomas George Stevenson, compiled a bibliography of his works, Bibliography of James Maidment, Esq., advocate, Edinburgh; From the year M.DCCC.XVII to M.DCCC.LXXVIII. Edinburgh: Printed for private circulation, 1883 (A new ed. of his "Bibliographical list of the various publications by James Maidment ... 1817-1859." Edinburgh, 1859.) 
- This article incorporates text from a publication now in the public domain: Wood, James, ed. (1907). "article name needed". The Nuttall Encyclopædia. London and New York: Frederick Warne.
- This article incorporates text from a publication now in the public domain: Hadden, James Cuthbert (1893). "Maidment, James". In Lee, Sidney. Dictionary of National Biography 35. London: Smith, Elder & Co.