Williams succeeds Mark McCall who resigned from the position in November following Ulster's heavy defeat to Gloucester in the Heineken Cup.
Williams accepted the job on Sunday morning, having been given the festive period to consider the offer following interview before the Christmas break, and Chief Executive Michael Reid informed the management team and the players immediately at a squad meeting at Newforge ahead of training.
Williams is expected to arrive in Belfast for a short visit later this week when it is anticipated that he will meet some players, hold a press conference with local media and watch Ulster in action against Munster in the Magners League at Ravenhill on Friday night, before returning to Australia to tie up some of his affairs.
Caretaker Coach Steve Williams will remain in charge of team affairs for Ulster's next three matches - against Munster in the Magners League and the back-to-back Heineken Cup matches against Bourgoin and Gloucester - before Matt Williams arrives permanently in the province at the end of January.
After the Heineken Cup match against Gloucester on the 20th January, Ulster do not have another game until they entertain the Dragons at Ravenhill in mid-February, and the natural break in fixtures will provide Williams with an ideal opportunity to settle in.
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