Former People sports editor Lee Horton has been ordered to repay more than £376,000 to his employers which he is accused of taking from them over a period of seven years.
Horton was fired in September after an internal investigation into allegations of financial irregularies. The police are are also involved in the matter.
The extent of the alleged fraud has only now become public with details of the civil court judgment.
In addition to the judgment against Horton, Mirror Group Newspapers is suing his wife Teresa for repayment of at least £136,715 which it claims he paid to her.
Press Gazette has learned that the paper won a High Court judgment against Horton in September, when he was ordered to repay £371,880 plus interest.
According to the latest High Court writ, between January 2001 and May 2007, Horton authorised three cheques for £36,470, £15,805 and £69,045 to be paid to TB Harding, Miss T Harding and T Harding. His wife's maiden name was Harding, according to the writ.
Horton, the writ says, authorised the cheques dishonestly and in breach of fiduciary duty. The cheques were then posted to an address in Canning Town belonging to his mother-in-law, and cashed - the writ says.
Horton also authorised more than 50 cheques, totalling £15,395, to be paid to Wymans, which was the name of an account held with his wife at Barclays Bank, Between October 2006 and August 2008, the writ also states.
The writ goes on to state that Mrs Horton knew that was receiving the money in her bank accounts over seven years, and there was no genuine reason why MGN would be making any payments to her, either in her maiden name or that of Wymans.
The publishers argue that she did not provide any goods or services to them, and was not entitled to any money.
She knew her husband was authorising the payments, as there was no-one else who was reasonably likely to be authorising them, the writ claims.
MGN contends that if the payments were legitimate, there could be no reason why they would be paid into her bank account rather than her husband's.
Mrs Horton either knew, or wilfully shut her eyes to the source of money, the writ says.
The publishers also accuse her of dishonestly assisting her husband's misappropriation by allowing him to use her bank accounts. Now MGN is seeking declarations that she is a constructive trustee of the payments, repayment of the money, tracing orders, and compensation with interest at a 'wilful default'rate.