In 1893, John Duff, together with some local businessmen, founded Longmorn Distillery. In 1876, he had built Glenlossie Distillery a quarter mile away; his family owned land at Miltonduff extending westwards to the opposite bank of the River Spey, and would establish BenRiach Distillery next door two years later. The distillery's location was close to excellent water sources and a railway. The site had previously been a 16th-century mill, and before that, an ancient chapel. The distillery only lasted five years. With the collapse of Pattison's of Leith and the sharp downturn of the entire industry, John Duff had to relinquish control of Longmorn and BenRiach, and by 1901, the remaining board members included J.A. Dewar (John Dewar & Sons), Arthur Sanderson (VAT 69 blended whisky), and James Anderson (J.G. Thompson of Leith). In 1899, management passed to James R. Grant, and later to his two sons, who were known as the 'Grants of Longmorn'; in 1970, they merged with the Grant family of Glenlivet and the Grant family of Glen Grant, along with Hill Thompson & Company, to form Glenlivet Distilleries Ltd, which was acquired by Seagram's in 1977. The distillery was expanded to 6 stills in 1972, and again to 8 stills in 1974, but its appearance has changed little over the years. Seagram's was acquired by Pernod Ricard Group in 2001, and Longmorn is now operated by its subsidiary, Chivas Brothers. In 2013, the group built a new mashing house and fermentation house at Longmorn, equipped with new Briggs lauter mash tuns and 2 additional fermentation tanks, increasing production capacity from 3.5 million liters of pure alcohol to 4.5 million liters.

A railway line connected Longmorn Distillery with BenRiach Distillery and operated until 1980. A 'puggie' (monkey) internal combustion locomotive transported malt from BenRiach to Longmorn. The locomotive is now preserved in Aviemore. The name Longmorn originates from a 7th-century English saint named Elan; a church dedicated to him was named 'Lannmoeran,' meaning 'the beloved Saint Elan's hermitage.' Another theory traces it to Saint Marnoch (or Maernog), who died in 625; many Scottish towns hold commemorative activities on this day, including Kilmarnock in East Ayrshire, Scotland. A third source suggests the name derives from 'Lhanmorgund' (land of the saints). Longmorn is described as 'the blender's second choice' (the first being their own distillery's product!), a view I know a retired master blender heartily agrees with!