"Sunset at Montmajour," a hilly landscape at dusk with the ruins of a Benedictine abbey in the background, was created in the same period when he made some of his most recognizable works, including "The bedroom," and "Sunflowers."
While the museum declined to reveal how the painting was discovered, it said it was owned by a Norwegian man who did not know its origins and put it in his attic.
In particular, the ambitious size and late period date of "Sunset" make it an important addition to Van Gogh's known oeuvre.
"A discovery of this magnitude has never before occurred in the history of the Van Gogh Museum," the museum's director, Axel Rüger, said in a statement. "It is already a rarity that a new painting can be added to Van Gogh's oeuvre."
"Sunset" measures 93.3 cm by 73.3 cm, and while Van Gogh works do emerge occasionally, nothing approaching this size has surfaced in almost 100 years.
Still, extensive research by the museum's art historians lead to a high level of certainty that the painting was indeed genuine.
"We carried out art historical research into the style, the depiction, the use of materials and context, and everything we found indicated that this is a work by Van Gogh," the museum said.
They were able to identify the painting's location, in an area of Arles where Van Gogh spent time exploring during the summer of 1888.
“There are, in hindsight, many pointers in his letters and entries in catalogues of the 1900s that have been linked to other paintings or misidentified," Fred Leeman, the former chief curator of the Van Gogh Museum and a Van Gogh scholar told the New York Times. "Here, we see a painting that fits those descriptions exactly."
"And what also contributes to the proof is the advances in research that have been done with the pigments, and the new evidence is completely in harmony with what we expect from this painting," Leeman said.
The museum said it was able to identify the pigments used in the painting's characteristic brush strokes as appropriate to the palette Van Gogh used for other works in the period, and used X-ray and computer analysis to identify the painting's canvas.
Letters written by the artist helped narrow down the painting to an exact date -- July 4, 1888 -- and helped trace its path after his death. Van Gogh's younger brother Theo had the painting in his collection in 1890 and it was sold in 1901.
"Sunset at Montmajour" will be shown at the Van Gogh Museum in an exhibition beginning September 24.