Dominic Chappell, who was in charge of BHS when it went bust in 2016, has been found guilty on three charges of failing to provide information demanded by The Pensions Regulator.
The watchdog accused him of neglecting or refusing to hand over information about BHS's pension schemes.
The schemes had 19,000 members and a shortfall of £571m when BHS collapsed.
Mr Chappell, a former bankrupt, bought the department store chain from Sir Philip Green for £1.
The Pensions Regulator (TPR) alleged that Mr Chappell failed to provide information three times about the company's pension schemes.
Appearing at Brighton Magistrates Court, Mr Chappell argued that he didn't have the information available because he had been shut out of his office at BHS after administrators took over.
He also said tax officers had raided his home, removing computers and files.
However the judge, Mr William Ashworth, said that he was not a credible witness, that parts of his explanation made no sense and that other evidence he offered was simply not credible.
Nicola Parish, TPR's executive director of frontline regulation, said: "Dominic Chappell failed to provide us with information we had requested in connection with our investigation into the sale and ultimate collapse of BHS, despite numerous requests.
"The power to demand specific information is a key investigative tool in our work to protect people's pensions. This conviction shows that the courts recognise its importance and that anyone who fails to co-operate with our information notices risks getting a criminal record."
Speaking outside court, Mr Chappell said he would appeal against the verdict.
He said: "As you can imagine, I'm extremely disappointed and annoyed about the outcome. It's not the one we were looking for.
"I've instructed my legal team to put in an immediate application for an appeal on this case, which we will be doing tomorrow."
He added: "We feel that this case has not been treated fairly and we will look deeply into this."
Unlimited fines
The offences he has been found guilty of carry unlimited fines for each count.
The judge has adjourned to a later date, 19 January in Winchester, to consider the financial aspects.
The highest previous fine in a case such as this was £5,000.
Administrators were called in to BHS after only a year under Mr Chappell's ownership, leaving 11,000 people out of work and endangering the pensions of 19,000.
The Pensions Regulator is said to be seeking £10m from Mr Chappell to shore up BHS's stricken pension fund, to add to the £363m already obtained from Sir Philip.
A spokesman for the regulator said: "Our separate anti-avoidance action against Dominic Chappell continues.
"TPR's determinations panel is considering evidence submitted by various parties and is expected to be in a position to issue its written determination notice to affected parties in the coming weeks."
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