Carol Hawkins, who had worked for Clayton for 17 years, was convicted on 181 counts of theft from Clayton's bank accounts over a four-year period.
Hawkins told Dublin's Circuit Criminal Court that Clayton authorised her spending, which funded trips abroad, a new car, university courses for her children and the purchase and maintenance of 22 thoroughbred horses, reports Sky News.
However, Clayton claimed that he was unaware of the purchases and only gave the PA access to his accounts in order to pay bills related to his Dublin mansion.
Hawkins was revealed to have written 181 cheques to deposit cash into her own account, a joint account with her then husband, and a credit card account.
The theft emerged in 2008, when the aide confessed to booking herself over £10.5k (€13k) worth of flights to visit her children in the US and London using Clayton's account. Further investigations then revealed the extent of her spending, including thousands of euros on holidays and clothes from designer boutiques in New York.
After a unanimous verdict, Judge Partick McCartan released 48-year-old Hawkins on bail with a sentencing hearing scheduled for July 6.
"The evidence in this case was overwhelming," McCartan told the jury. "Nobody could seriously disagree with the verdict you have given."
The prosecution described the case as a "grubby tale of prolonged, repeated and pernicious fraud and gross mistrust".
Clayton said after the verdict: "I welcome today's outcome and I wish to thank the jury, An Garda Siochana and all those involved in the case.
"I would [also] like to thank my family and friends and colleagues for their support."
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