Ramesh “Sunny” Balwani, a Silicon Valley executive, was found guilty of defrauding investors as part of a scheme with his ex-girlfriend Elizabeth Holmes.
He constantly and fraudulently asserted that Theranos, their company, had a technology that could identify hundreds of diseases from a few drops of blood.
In a separate trial held in January, Holmes was convicted guilty of the abuse claims she had made against Balwani, who has denied them.
In the fall, a court will sentence Holmes, 38, and Balwani, 57.
Holmes is currently out on bail and could spend up to 20 years in prison. Balwani could spend up to 20 years behind bars and pay his victims millions of dollars in damages.
Theranos once had a market value of $9 billion (£7.5 billion), but its blood-testing technology was ineffective.
In the heart of Silicon Valley in San Jose, California, on the fifth day of jury deliberations, the verdict was announced. All 12 of the accusations made against Balwani were found to be true.
Prosecutors displayed text conversations that Balwani had sent to Holmes during closing statements on June 21.
In 2015, he stated “I am responsible for everything at Theranos,” he wrote in 2015. “All have been my decisions too.”
Jeffrey Schenk, an assistant US attorney, described the communication as an admission of guilt. He declared, “He’s acknowledging his role in the fraud,”
