Federal police in the western city of Saarbrücken said the woman reported the highly rare instrument missing after she left it in the luggage compartment of a train coming from the city of Mannheim, about 130 kilometres (80 miles) away.
Quick checks with the railway company revealed that the car in which she had been sitting had been attached to a train returning to Mannheim.
"One minute before the train's departure, the violin case was found in the last compartment and the musician, who was more than relieved, was able to reclaim it after verification it was her property," police said in a statement.
"Her relief was well founded as the violin was a General Dupont Grumiaux Stradivarius dating from 1727 and worth €2.4 million", the statement added.
Around 550 of the highly coveted violins handcrafted by Antonio Stradivari still exist, experts say, out of a total 1,100 by the 17th century Italian master craftsman.
They are highly prized for their incredible - and inimitable – sound. Many have experienced some remarkable adventures over the centuries.
In January 2014, a Stradivarius was snatched from the concertmaster of the Milwaukee Symphony Orchestra in Wisconsin by muggers armed with a stun gun. It was recovered in a matter of days.
In July 2012, a Stradivarius was turned in to a Swiss railway lost-and-found counter after an acclaimed violinist forgot it on a commuter train.
And in 2008, an American violinist left a $4 million Stradivarius in the back seat of a New York taxi. The driver returned it to its owner.