Gaffney will begin working at Franklin’s Gardens on New Year’s Day ahead of the home Aviva Premiership match against Gloucester on January 6.
The 70-year-old is one of Australia’s most experienced coaches who will bring more than two decades of professional coaching experience to Saints.
Gaffney will already be a household name to supporters of Irish rugby after spells with the Munster, Leinster, and Ireland squads between 2000 and 2011.
As backs coach of the Ireland national team and Leinster in 2009, Gaffney helped to mastermind both a Six Nations Grand Slam triumph and a Heineken Cup victory in the same year.
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Since then, the Australian served as senior assistant coach at the New South Wales Waratahs from 2011 to 2013, and has been Rugby Australia’s national elite programmes coach from 2013 to present.
Saints have been in the market for both short-term and long-term options to fill the void left by director of rugby Jim Mallinder, who departed earlier this month.
And Gaffney will now oversee the existing coaching team of acting head coach Alan Dickens, forwards coach Dorian West, Phil Dowson, who will now oversee defence having previously been transition coach, and assistant coach Mark Hopley.
“We are delighted to have recruited Alan as our technical coaching consultant until the end of the season,” said Saints CEO Mark Darbon.
“Alan is hugely experienced and admired throughout the game for being a forward thinking, innovative rugby coach.
"His CV speaks for itself; he has been successful with some of the best teams in the world – including winning a Six Nations Grand Slam and Heineken Cup – and has a clear understanding of how to set-up an effective all-around rugby team.
"He also has a proven track record of developing some of the world’s best coaches and players.
“Alan will take on responsibility for the rugby department and will lead the existing coaching group made up of Alan Dickens, Dorian West, Mark Hopley and Phil Dowson.
“In parallel, the board will continue to focus on the recruitment of a permanent director of rugby to be in place for the start of the 2018/19 season.
"As I have said previously, there has been a great deal of interest in this vacancy and we hope to be able to announce this appointment in the coming months.”
After making more than 200 appearances for Sydney outfit Randwick as a player, Gaffney began his coaching career at his home club before getting his break as assistant coach at the NSW Waratahs in 1997.
During his time at Randwick, Gaffney coached current Australia boss Michael Cheika and England’s Eddie Jones – forging a relationship that saw him work as Jones’ assistant coach with the Australian national team.
From there, Gaffney moved to Saracens where he was director of rugby from 2006 to 2008, guiding the north Londoners to the Aviva Premiership play-offs for the first time ever in 2007 and their first Heineken Cup semi-final in 2008.
That appointment followed initial spells with Leinster as backs coach and then Munster as head coach from 2000 to 2005, where he won back-to-back Celtic League titles.
“I am really excited about the challenge ahead,” said Gaffney.
“Any coach would jump at the chance to work with the calibre of players Saints have.
"The squad have shown what they’re capable of earlier in the season but, for whatever reason, they have not been able to perform at that level consistently.
“I’m looking forward to working with Alan Dickens, Dorian West, Mark Hopley, Phil Dowson and the rest of the backroom staff from the start of the new year.”