His lawyer Dominique Tricaud read a handwritten note found at Germain’s home to the court Tuesday, the opening day of the trial, describing it as a “farewell letter”.
"I can’t accept being prosecuted for abusing my power, nor accept this political game. You can be assured I have never stolen one centime. My close family and friends will understand," it said.
Police sources have told AFP that the death is being investigated as a suicide.
Germain, a member of President Francois Hollande’s parliamentary majority, was due to stand trial for his alleged complicity in collusion and misappropriation of public funds.
A member of his staff who worked in tourism, Lise Han, was also running a private company which brought Chinese tourists to visit Loire Valley castles and take part in symbolic wedding ceremonies with Germain.
Hundreds of Chinese couples came to France for the experience between 2007 and 2011.
Han was arrested on embezzlement charges in 2013 in what became known locally as the “Chinese weddings affair”.
Germain had said he was in the dark about the "lies and manipulations".
Tricaud told AFP he was “overwhelmed” over the discovery of Germain’s death.
"The last time I saw him was last week. He said that no one in his family had ever stood accused in court ... he saw it as a sort of dishonour," the lawyer added.
French Prime Minister Manuel Valls told French press Tuesday that he had “lost a friend”.
"I knew he had to face a tough time in this trial," he said. "I thought he had the strength and determination to be able to confront justice."