A senior staff member at Catholic Superannuation Fund failed to declare that businesses associated with his brother and wife were winners of lucrative million-dollar-plus marketing contracts in a major breach of conflict of interest rules, the royal commission has heard.

Catholic Super general manager investor relations Rob Clancy failed to disclose that his brother and wife were shareholders or directors of companies that picked up plum contracts from the industry super fund that holds $9 billion of funds on behalf of mainly teachers within the Catholic sector, the royal commission has heard.

Mr Clancy has been put on leave as Catholic Super reviews the matter, the royal commission heard on Wednesday.

Mr Clancy's brother Paul Clancy's company Australian Family and other companies associated with Paul Clancy and Rob Clancy's wife Jennifer Kernahan won contracts of up to $2 million from the superannuation fund.