Theranos founder Elizabeth Holmes has been found guilty of four charges of fraud at a trial in California.
Prosecutors argued Holmes knowingly lied about her blood-testing firm and technology able to detect diseases with just a few drops of blood.
Jurors found Holmes guilty of four charges, including conspiracy to commit fraud against investors and three counts of wire fraud.
The 37-year-old could face up to 20 years in prison.
Holmes was found not guilty of four other charges, including knowingly lying to the public. The jurors were unable to reach a verdict on three other counts they were considering.
The split verdict came after the judge said the jury, having deliberated for seven days, could deliver a partial verdict.
Theranos, at one point valued at $9bn (£6.5bn), was once the darling of Silicon Valley.
The firm promised it would revolutionise the healthcare industry, but it began to unravel in 2015 after a Wall Street Journal investigation reported that its core blood-testing technology did not work. It was was officially shuttered in 2018.
For nearly four months at trial, the jury of eight men and four women were presented with two starkly different accounts of the former self-made billionaire, whose downfall shook Silicon Valley.
Calling some 30 witnesses, prosecution sought to prove that Ms Holmes knew the product she was selling to investors was a sham, but remained hell-bent on the firm’s success.
At trial, multiple lab directors testified they told Holmes about the flaws in Theranos’ technology but were instructed to downplay their concerns. At the same time, they said, Holmes told investors the technology was operating as planned.
Holmes “chose fraud over business failure. She chose to be dishonest with investors and patients”, said prosecutor Jeff Schenk in closing arguments. “That choice was not only callous, it was criminal.”
But the defence countered with descriptions of a dedicated and driven businesswoman, making waves in a male-dominated industry.
“You know that at the first sign of trouble, the crooks cash out, criminals cover up and rats flee a sinking ship,” defence attorney Kevin Downey said last week. But Holmes stayed, he said, and she “went down with that ship when it went down”.
Testifying in her own defence, Holmes acknowledged mistakes in Theranos’ operation, but maintained she never knowingly defrauded patients or investors.
The defence also laid blame on Ramesh “Sunny” Balwani, Holmes’ former business partner and long-term boyfriend.
Holmes has accused Mr Balwani, 19 years her senior, of emotional and sexual abuse. Over seven days on the stand, she described an intense relationship, in which Mr Balwani controlled how she ran Theranos, who she spoke to, how she spoke to them, and what she ate. He has denied the allegations.
Their decade-long relationship came to an end around the same time he stepped down as CEO in May 2016. He faces a separate trial next month.
Holmes founded Theranos at age 19, shortly after dropping out of chemical engineering at Stanford University. She was able to raise more than $900m from billionaires such as media magnate Rupert Murdoch and tech mogul Larry Ellison.