Two improbable Britons brought the line into being. David James, the politician-soldier who owned Torosay Castle, decided in 1975 to open the house and gardens to the public. The problem was practical: visitors stepped off the CalMac ferry at Craignure pier, looked up at the rain-soaked road, and saw the castle nowhere in sight. Graham Ellis, a local businessman and a railway enthusiast, suggested an answer. Build a narrow-gauge line from the ferry to the castle gates. Let the journey itself become an attraction. Planning permission arrived the same year, but construction did not begin until April 1982. The line was finished in May 1983, and the first paying passengers climbed aboard on 18 August that summer. The official opening followed a year later, on 22 June 1984. Scotland's original island passenger railway was open for business.

Six engines worked the line over its lifetime, and each had a story. Lady of the Isles, built in 1981 by Roger Marsh, was a 2-6-4 tank engine that had previously hauled holidaymakers around a Suffolk amusement park. Victoria, completed by Mouse Boiler Works in 1993, was modelled on the Baldwin-built Victorian Railways NA class - the same lineage as the celebrated Puffing Billy engines in Australia. Waverley, the oldest locomotive on the line, had been built by David Curwen in 1948 and originally named Black Prince. The diesels were stranger still: Glen Auldyn was hand-built on Mull by Bob Davies in 1986, powered by a Perkins engine cannibalised from a Commer van. When the BBC children's series Balamory drew a wave of family visitors to nearby Tobermory, Lady of the Isles ran with a special headboard renaming her the Balamory Express. Up to 2010, the line carried more than 25,000 passengers a year.

The end came not from any failure of the railway but from the castle it served. In 2010, Torosay went up for sale, and the railway company - which leased its land from the estate - could not promise its passengers the journey's destination would still welcome them. Formal closure was announced on 28 October 2010. On the final running day, 4 December 2010, Caledonian MacBrayne offered discounted ferry tickets and printed commemorative posters. Graham Ellis and Martin Eastwood, the line's founders, drove the last train themselves - a double-headed special with Lady of the Isles and Victoria pulling every carriage on the line. A brief reprieve came the following summer, when limited services ran until 1 September 2011. Then the locomotives were trucked away. The track was lifted in October 2012. Most of the engines now live at Rudyard Lake Steam Railway in Staffordshire, where they meet once a year for the Isle of Mull Gala to remember what they used to be.