O'Brien's wife collapsed as the verdicts were read and was taken to a hospital.
He faces a long term in federal prison when he is sentenced in November.
Prosecutors charged that O'Brien used jobs as bribes for members of the Massachusetts legislature, hiring lawmakers or their candidates. In return, he allegedly got huge increases in his budget.
"None of these legislators worked a day at probation," Assistant U.S. Attorney Robert Fisher said during a hearing in December on a defense motion to dismiss the indictment. "They did nothing for probation."