The 55 year old Australian only became a contender after Williams had successfully negotiated a fresh contract with Leinster, the province declaring less than a week ago they were confident of retaining the services of Gaffney.
However, the lure of being number one to one of the most consistent performers in European rugby proved too much and Gaffney now steps center stage.
The move south ends a long working relationship between him and Matt Williams. A former player and coach at the famous Randwick club in Sydney, Gaffney is one of only 15 life members, honoured for his distinguished service to the club, Gaffney coached the New South Wales Under-21 backs and then the NSW Waratahs' backs as assistant to Williams in the Super 12 for three seasons, before they renewed their partnership two years ago in Ireland.
Speaking about the appointment, Munster Chief Executive Garrett Fizgerald said. " We are delighted that negotiations to fill the postion have been brought to a successful conclusion. We welcome Alan Gaffney and wish him every success. We are also pleased that with the position now filled it allows Declan and Niall concentrate fully on preparing the side for the latter stages of the Heineken Cup and Guinness Interprovincial Championship."