More than 60 years after taking the rare books, former army soldier Robert Thomas handed them over to German ambassador Klaus Scharioth at a ceremony at the National Archives in Washington.
One of the books, published in 1573, dealt with Prussian statutes, while the other was a 1593 illustrated commentary on Roman law.
Thomas recalled how as a young infantry soldier more than 60 years ago, he stumbled into a "huge room that was filled with thousands of books from the floor to the ceiling."
Like many valuable artworks and a trove of Nazi Germany's gold and monetary reserves, the books had been stowed in an underground mine in the town of Merkers, near Frankfurt.
Thomas brought the books as souvenirs back to the United States at the end of the war.
"I kept them in two boxes in the darkest and coolest place at my house in order to preserve them. They are pretty much in the same condition as I found them," said the now 83-year-old.
He recently contacted the National Archives, who traced the books' owners and urged Thomas to return them to Germany.
"The books will go home now. That's the right thing to do," Thomas said Tuesday as he handed the tomes to Scharioth.
The German ambassador said the books would return to the shelves of the Diocesan Museum of Paderborn and the University of Bonn library, which owned them before the war.
"It's such a 'Glücksfall' for Germany that we have these books back," he said, using the German word for "stroke of luck."
"The fact that these books are returned tells you a lot about our relationship today - it's a sign of friendship and trust," Scharioth said.