A young Liberal who is managing Christine Forster's campaign to become Sydney's next lord mayor had to repay almost $14,000 to his former charity employer after it was discovered he had charged personal expenses to the organisation's credit card.

Mitchell Price, who is also a senior adviser to Coogee MP Bruce Notley-Smith MP, used a corporate credit card to purchase $13,816 of personal hire-car travel and social media and Facebook advertising while employed as an executive assistant to the CEO of Sydney Gay and Lesbian Mardi Gras from November 2013 to April 2015.

Mr Price, whose sudden departure from the organisation was subject to a confidentiality agreement, told Fairfax Media he had "mistakenly" charged his personal expenses to the charity's corporate credit card.

He attributed the mistake to an inadvertent linking of the charity's corporate credit card to accounts on his computer.