Williams is to use his expertise to assist with player contracts - for both senior and youth players.
Speaking of the news, Chief Executive Office Garry Cook told the club's website:
"John Williams is a hugely respected figure in the football world and I admire him greatly. Unsurprisingly, a number of organisations were keen to work with him and I was therefore delighted when he accepted my offer to join us.
"We must ensure that our targets are not impacted by the high volume of daily operational tasks. John's support of Brian and the football operations team will enable us to ensure those targets are met and he will be a great asset to the club."