Mendelssohn wrote the privately commissioned piece, titled The Heart of Man is Like a Mine, in 1842.
It was never published but the original manuscript has now emerged in a private collection in the US.
The song was performed exclusively for the BBC’s Radio 4 Today programme by Christopher Glynn and Amy Williamson from the Royal College of Music.
It comprises just 29 bars for an alto voice and piano in A flat major.
It was a private commission for an acquaintance who worked at the Court Theatre in Berlin.
Christie’s senior specialist in manuscripts Thomas Venning said before the BBC performance: “This is a very exciting rediscovery: the song was only ever a private commission and we know that even in Mendelssohn’s lifetime he deliberately prevented its circulation.
“The manuscript has been lost for 140 years, so it seems likely that we have here music by one of the great composers that no living person has ever heard. It is quite a simple, short song with a catchy, lilting melody. I can’t wait to hear it played.”
Peter Ward Jones, a renowned Mendelssohn scholar, told Today the piece was significant: “It’s lovely to hear it. All composers have their better days and their off days [but] this is certainly not one of Mendelssohn’s off days.”
The manuscript has the composer’s customary signature at the bottom, which proves the piece is genuine.
The text of the song is drawn from the second stanza of Friedrich Ruckert’s poem Das Unveranderliche and compares the human heart to a mine which can produce gold, silver or humbler ore, but only gives what contains within itself.
Although never published, the song was known to scholars as it had been sold at auction in 1862 and again in 1872.
Since then, its whereabouts were unknown until it was found in the papers of the current owner’s grandfather, himself a musician and Mendelssohn enthusiast. But how and why the piece came to be in the US is still a mystery.
The song is accompanied by a letter from Mendelssohn to theatre manager Johann Valentin Teichmann – who commissioned the song – asking him not to circulate the piece.
Given it was a private commission, Ward Jones said Glynn and Williamson’s rendition was “almost certainly the first public performance of this song – Mendelssohn would probably have disapproved [because it was written as a private commission]”.