The five paintings, by German and Flemish masters, had been missing since World War Two. Three were won in a poker game by an American GI who mailed them home to his family in the US.
Two others were bought by an American woman serving as a librarian in the US Special Services after the war, according to the Monuments Men Foundation.
The foundation's work was highlighted in George Clooney's film, which portrayed the team of museum directors, curators, and educators deployed to prevent the destruction of historic treasures during the war (photo).
During a ceremony at the US State Department on Tuesday, German Ambassador Peter Witting thanked the families and Robert Edsel of the Monuments Men Foundation: "You can be assured these paintings come home to a worthy setting."
Edsel said how the paintings got to the US was no longer the issue: "Seventy years have passed," he commented. "We are focused on returning them to their rightful owners."
The works mailed by the GI, a decorated US Army major, were by the Flemish Baroque painter Frans Francken III, the German painter Christian Wilhelm Ernst Dietrich and Austrian artist Franz de Paula Ferg. They had been hidden in a potassium mine by an art gallery in Dessau.
A member of the major's family saw the Monuments Men film and contacted Edsel, who wrote the book on which the film is based, at the foundation.
The two paintings belonging to the librarian, Margaret Ingeborg Reeb, who died in 2005, were the property of Empress Friedrich of Kronberg Castle near Frankfurt. She was a daughter of England's Queen Victoria.
One of the paintings showed Queen Victoria with her daughter, the other was a portrait of King Charles I, attributed to Anthony van Dyck in 1636. The paintings had spent the intervening period in a bank deposit box in Montana.
Edsel praised the families for the care they had taken of the artworks and said he understood the resentment one of the relatives felt towards Germany, which had initially kept him from returning the paintings.