Balwani was convicted on two counts of conspiracy and 10 counts of fraud, a spokesperson for the US Attorney’s Office confirmed.
An attorney for Balwani did not immediately respond to a request for comment.
The jury in San Jose, California, handed down its verdict after deliberating for a little more than five days.
Theranos founder Elizabeth Holmes, who initially faced the same charges, was convicted on three counts of fraud and one count of conspiracy at a separate trial in January.
Balwani and Holmes were charged in 2018 with lying to investors about the company’s finances and its machines’ ability to run a broad range of tests from a few drops of blood. Prosecutors also charged the pair with duping patients about the tests’ accuracy.
They were granted separate trials after Holmes said she would testify that Balwani was abusive towards her in their romantic relationship. Balwani has denied the allegations.
Theranos investors were drawn to Holmes after her promise to upend the laboratory testing industry by creating portable machines that could run a broad array of tests.
The company touted work with drugmakers, pharmacies and the US military, and received investments from well-known media businessman Rupert Murdoch.
Theranos collapsed after The Wall Street Journal published a series of articles, starting in 2015, that suggested its devices were flawed and inaccurate.
At trial, Holmes made the somewhat unusual decision to testify in her own defence and denied lying to investors.
She is scheduled to be sentenced on 26 September. She has argued that the evidence was insufficient to support the verdict.
(Reporting by Jody Godoy in New York; Editing by Noeleen Walder and Howard Goller.)