The painting, which depicts an elderly Jewish woman selling oranges on a Warsaw street, was unveiled by the Culture Ministry after it had been listed as missing for 60 years.
'We got it back after so many years. ... It's a great celebration and gift for the museum,' said Agnieszka Morawinska, the museum's director.
Historians think A Jewish Woman Selling Oranges was likely looted in the final days of World War II when Nazi soldiers occupied the museum building. The painting had suffered damage after it was taken out of its frame and rolled up.
'It's a great miracle that we got it,' said Anna Lewandowska, a museum conservator. 'What it didn't lose is its spirit and its genius.'
The painting was discovered after it was put up for sale in a little-known auction in November in Buxtehude, Germany, near Hamburg.
The painting was withdrawn from sale after Polish prosecutors intervened.
'For me there was one most important thing: that the painting be returned to Poland,' Culture Minister Bogdan Zdrojewski said.
The auction house owner said she was not aware the painting had been on Poland's list of stolen art works, and had offered it for a low price of 4,400 euros because she doubted it was genuine.
Poland launched negotiations with the painting's owners in December, and those went on for seven months before the painting was returned to Warsaw on July 15.
Painted by the prominent 19th century Polish impressionist Aleksander Gierymski, the painting depicts a scene from before World War II when Warsaw boasted a large Jewish population.