Disgraced former Liberal MP Tim Owen has repaid $50,000 following an investigation by the NSW electoral commission into donations he received before the 2011 state election.

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.