In a statement on Monday, the electoral commission said an investigation had found that nine unlawful donations totalling $84,137.60 were made for Mr Owen's benefit.

They included $20,000 in cash donations to Mr Owen's campaign director, Hugh Thomson.

The commission said Mr Owen failed to declare the donations, as required, and had agreed to pay back $50,000 of the $64,047.60 in donations "without admission" after being sent a letter of demand in August last year.

Mr Thomson had repaid $20,000, also "without admission", the commission said.

The donations were deemed unlawful as they were from prohibited donors, above the donations cap and classified as indirect campaign contributions.

Among the donations received by Mr Owen was $10,000 in cash from property developer and former Newcastle lord mayor, Jeff McCloy.

Property developers have been prohibited from donating to NSW campaigns since the end of 2010.

Last year, the commission announced another disgraced former Liberal MP, Andrew Cornwell, had repaid $10,000 cash he received from Mr McCloy during the 2011 election campaign.

The commission's investigations follow the Independent Commission Against Corruption's Operation Spicer hearings into Liberal party fundraising, during which Mr Owen and Mr Cornwell resigned from parliament.

Last September, the commission said the NSW Liberal Party had been forced to forgo almost $600,000 in public funding after political donations equal to that amount, channelled through a Liberal-aligned entity called the Free Enterprise Foundation before the 2011 election, were deemed to have been unlawful.

In its statement on Monday, the commission said it had concluded its investigations following Operation Spicer and had recovered a total of $666,992 in unlawful donations.

However, it also said it had been advised there was insufficient evidence that two other former Liberal MPs, Chris Spence and Darren Webber, had received unlawful donations from property developers via a business, Eightbyfive.

During Operation Spicer, the ICAC heard that Eightbyfive was established by Tim Koelma, who after the 2011 election became a policy adviser to former energy minister Chris Hartcher.

In its report tabled last August, ICAC found Mr Koelma and Mr Hartcher used Eightbyfive to receive and channel political donations for the benefit of Mr Hartcher, Mr Spence and Mr Webber "with the intention of evading the election funding laws".

These included payments from Australian Water Holdings, Gazcorp and Nathan Tinkler's Patinack Farm horse stud.

But the electoral commission said the Crown Solicitor had advised there was "insufficient evidence" that the donors were property developers or the payments were political donations as defined by NSW election funding laws.

Under the laws, a company must regularly submit development applications to be considered a property developer.