Sir Haydn was built in 1878 by Hughes' Loco and Tramway Engine Works Ltd. of Loughborough as a 0-4-0, currently a 0-4-2ST. He currently lives on the Talyllyn Railway.
He worked on the nearby Corris Railway until the closure of that line in 1948. In 1951, he was purchased by the Talyllyn Railway, along with the other surviving Corris locomotive, who became Edward Thomas, and was named after the line's late owner, Sir Henry Haydn Jones. The precarious state of the track meant he was seldom used for the first few years, and firebox problems caused his withdrawal in 1957. He re-entered service in 1968.
In 1982, Sir Handel visited the Talyllyn Railway to help tide over a locomotive crisis while Sir Haydn was being repaired. In 1984, Sir Hadyn returned to service and Sir Handel was returned to the Skarloey Railway.
In April 2012, Sir Haydn made his second visit to the Corris Railway and worked there until May 17, 2012 when his boiler certificate expired. However, he remained at the Corris Railway for the rest of the summer as a static exhibit to generate interest in the Corris Railway's plans for their next new-build locomotive; a copy of Sir Haydn. Sir Haydn is currently touring railways across Great Britain to raise funds for an overhaul. After this, he returned to the Talyllyn Railway in March 2015, where he had one final public appearance before going in for his overhaul. Sir Haydn was stored in the sheds at Pendre, awaiting a new boiler.
In Autumn 2015, Sir Haydn was transferred from the Talyllyn Railway to the workshops of the Vale of Rheidol Railway in Aberystwyth for his overhaul to be carried out. His overhaul was completed in April 2018 in time for his 140th anniversary.