A non-executive chairman is a role unconnected with the day-to-day management of a business and which is instead concerned with effective management of the board.
As a 'non-executive', the chair is impartial and can use this distance to maintain an objective position, albeit with the duty of representing the interests of all shareholders. As someone who is independent from the business they are also able to provide third party governance.
Non-executives tend to be very experienced professionally and must be able to hold the board to account in a sensitive manner in order to maintain effective management.
At Connection Capital it is usual for us to add a non-executive chairman to the board as part of a private equity transaction. The appointment will be mutually agreed between ourselves and the directors of the business.