The ruling conservative and Eurosceptic Law and Justice party has been pushing to nationalise important businesses and cultural artefacts, as part of a focus on national pride.
Minister of Culture Piotr Glinski said the sale "ensures the right of the Polish nation to the collection".
The Polish government has bought a world-famous art collection, including a rare Leonardo da Vinci painting, for a fraction of its market value.
The Czartoryski collection was sold for €100m ($105m; £85m) despite being estimated at about €2bn.
It includes Rembrandt and Renoir works, and Leonardo's Lady with an Ermine.
The head of the Czartoryski family, which owned the collection, said it was a "donation", but the board of its foundation resigned in protest.
The Czartoryski Foundation's management board said it was not consulted about the sale, which was negotiated between Poland's culture ministry and Adam Karol Czartoryski, a descendent of Princess Izabela Czartoryska, who founded the collection in 1802.
Mr Czartoryski, the foundation's head, said he was following his ancestors who "always worked for the Polish nation".
"I felt like making a donation and that's my choice," he said.
The collection is made up of about 86,000 artefacts, as well as 250,000 manuscripts and books. Most of the artworks are housed in the National Museum in the southern city of Krakow.
All are now the property of the Polish state.