Negro Soldier

By Robert Smullyan Sloan.

At Harvard Art Museums. 617-495-9400, www.harvardartmuseums.org

CAMBRIDGE — It’s not often that a work appears, unheralded, on the walls of one of our major museums and instantly establishes itself as canonical. It’s even rarer when the work is more than 70 years old, has not been displayed for more than 40 years, and is by an artist you’ve likely never heard of: Robert Smullyan Sloan.

This work, titled “Negro Soldier,’’ was painted in 1945. It was kept by Sloan in his own collection until nine years before his death, at age 97, in 2013. Sloan sold it directly to Harvard Art Museums, where it recently went on display.

Sloan is not listed in the five-volume Grove Encyclopedia of American Art. But he had a successful career as both an illustrator and a painter, and this is not the only work by him to make it into a major museum.

It is, however, the best.

It shows an unknown US Army private in a dress uniform adorned with two ribbons — one standing for good conduct, the other for participation in the European-African-Middle Eastern Campaign.

Sloan was himself drafted into the Army, in 1943, but he was not posted overseas. He was stationed in New York, where he worked as an illustrator for the armed services and US Treasury.

The astonishing portrait shows his subject sitting in a compressed space, squeezed between us and a window. Through that window we can make out an urban scene that is likely New York. There is a black truck loaded with coal, apartment buildings catching various degrees of light, and a run of down-at-heel shops at street level. One sign says “LOANS CASH’’; another has mannequins in the window display.

Welcome home, private, thank you for your service.

Even after fighting for their country in foreign theaters of war, African-American soldiers, if they were lucky enough to survive, faced hobbling prejudice back home. This picture, one might argue, illustrates that predicament.

But isn’t it too singular to be reduced to sociology? Sloan makes us feel so close to this man that we become acutely aware that his nose, the bulge of his tie, and the gleaming brass button at the center of his chest occupy pockets of space nearer to us than his eyes. Slightly recessed though they are, his eyes gaze out with a vulnerable pride that is haunting.

Sloan maintains an almost Flemish evenness of attention across the entire picture. This gives it a surface tension that either we or the vivid, light-catching protrusions of the soldier’s slightly turned face feel permanently on the verge of breaking.

We kid ourselves if we think we can know what this man is feeling, what he has experienced, or what his political views are. What is not in doubt is that he is a human vessel, full to overflowing.

Negro Soldier

By Robert Smullyan Sloan. At Harvard Art Museums. 617-495-9400, www.harvardartmuseums.org

Sebastian Smee can be reached at ssmee@globe.com.