He specialised in 15th-century and early Tudor history, and among other tasks edited the Letters and Papers of the Reign of Henry VIII series.
[1] and brother of Sir William Tennant Gairdner, he was born and educated in Edinburgh.
He entered the Public Record Office in London in 1846, remaining at work there until his retirement over fifty years later in 1900.
[2] In association with J. S. Brewer, Gairdner prepared the first four volumes (in nine parts) of the Calendar of Letters and Papers of the Reign of Henry VIII, and, after Brewer's death in 1879, Gairdner completed the series, with the assistance of R. H. Brodie, in 1910, in twenty-one volumes (in thirty-three parts), having calendared about a hundred thousand documents, from numerous sources, in several languages.
[2] He also wrote The Life and Reign of Richard the Third, which argued that the negative portrayal by Shakespeare and More was basically correct.