The lead sculpture, called Mother and Child, was believed to have been made by Moore in 1939-40 and will be auctioned in March.
The abstract depiction of two figures made from lead, called Mother And Child, was authenticated by Dreweatts auctioneers alongside experts from The Henry Moore Foundation, who traced it back to a sketch from 1939.
Dreweatts has said the piece was crafted in 1939-40, and had been a gift to the original owner, Hubert de Cronin Hastings, who was at that time the editor of The Architectural Review.
The auctioneers have valued the sculpture at an estimated £30,000 to £50,000, but said it could fetch much more when it is up for sale later this year.
The piece was given to Mr de Cronin Hastings via Moore’s friend Jim Richards, who was assistant editor of the same publication.
In the 1970s, it was passed down to his son, John Hastings, who kept it on his mantelpiece among an eclectic mix of objects until he died in 2019.
Dreweatts specialist Francesca Whitham described the sculpture as “unique and rare”, partly because Moore only briefly worked with lead in the 1930s.
She said: “It has been such a fascinating journey working with this rare Henry Moore sculpture.
“I was elated, after many months of delays due to Covid restrictions, to finally receive the letter from the foundation authenticating the piece as a genuine Moore.
“Dreweatts is honoured to bring this sculpture to the market for the very first time, presenting an opportunity to purchase a unique and rare sculpture by one of the most important British artists of the 20th century.”
Moore experimented with lead while working with rope and wire to create his famous stringed sculptures, and Mother And Child is believed to have been a preliminary design for a stringed piece.
The Henry Moore Foundation linked the work to a 1939 sketch by Moore from its records, titled Eighteen Ideas For Sculpture.
It will be offered in Dreweatts modern and contemporary art sale on March 16 this year.
Moore was born in Castleford a mining town in West Yorkshire in 1898, and after training to be a teacher and serving in the British Army he studied at Leeds School of Art and the Royal College of Art in London.
He is considered a pioneer of his craft, and was the first British artist to become globally recognised in his lifetime.
Moore’s sculptures are now seen as symbolising post-war modernism, and The Henry Moore Foundation credits his work with creating a British sculptural renaissance.