The Renaissance helmet and armor were made in Milan and inlaid in gold and silver, according to a statement from the Louvre on Thursday.
Baroness Salomon de Rothschild donated armor to the French state in 1922. The pieces were on display in the Louvre when they were stolen overnight from May 31 to June 1, 1983, according to the statement.
“The circumstances of the theft of these pieces, little known to the general public, had remained a mystery,” the museum said.
The “deeply disturbed” theft of the museum staff at the time, but the armor has now been recovered due to the work of investigators, according to the statement.
The armor will be displayed in the Objets d’Art rooms in the Richelieu wing when the Louvre reopens. It was closed to the public in October last year due to coronavirus blocking restrictions.

The armor will be exhibited at the reopening of the museum. Credit: THOMAS SAMSON / AFPGetty Images
Such thefts are rare, but not unheard of.
One of the museum’s most famous works was stolen more than 100 years ago.
Before the 20th century, Leonardo da Vinci’s “Mona Lisa” was not well known outside of art circles. But in 1911, a former employee of the Louvre kidnapped the portrait and hid it for two years.
The public fascination with theft contributed to the consolidation of the place of painting in the popular culture of that time.
“Mona Lisa” is one of the star attractions of the most visited museum in the world.
Last year, the Louvre lost more than 90 million euros ($ 109 million) in revenue and saw a 72% drop in visitors due to pandemic disruptions.
However, the museum makes the most of the closures by carrying out long-planned renovations.