Edwards joined the WRU national squad coaching team in 2008 on a part time bais and, alongside Gatland and fellow coaches Rob Howley, Robin McBryde and Neil Jenkins oversaw Wales' RBS 6 Nations Grand Slam in his debut season as an international coach.
The former Rugby League playing great, who captained England in both League and Union at schoolboy level, began his coaching career in Union alongside Gatland at London Wasps in 2001, where the duo won three consecutive Premiership titles and the Heineken Cup during the four seasons they were together.
In 2009 the pair, with the WRU's blessing along with Howley and Jenkins, coached the British & Irish Lions on tour to South Africa under head coach Sir Ian McGeechan.
Once Edwards returned from the 2011 Rugby World Cup in New Zealand which saw Wales reach the semi-final stages for only the second time in their history, negotiations with WRU Chief Executive Roger Lewis intensified as rugby institutions around the globe expressed their interest in his services.
"I concluded negotiations with Shaun over the week-end and am extremely pleased to be able to announce we have secured his services for the WRU up to and including the Rugby World Cup in 2015,"said Lewis.
"We have an outstanding team of coaches and back room staff working under WRU Head Coach, Warren Gatland, and Shaun's role as defence coach within that team is something quite unique.
"Talks began informally and discreetly in New Zealand with Shaun, and have continued over the past two weeks. I am particularly pleased to add that In addition to his extended senior national team duties under Warren, Shaun will also be working with WRU Head of Rugby, Joe Lydon, within the WRU National Academy.
"Shaun will work with the Wales U20's, 18's and 16's. This is part of our strategy to ensure our coaches have influence over our elite players early in their development."
"Under the terms of the contract Shaun will be released one day a week, save test match weeks, to work with an English Premiership club.
"However I have also negotiated the opportunity for Shaun to also work at times with Welsh Premiership clubs, which is particularly exciting for this level of our game.
"Our structures are in place both on and off the field to take us up to and beyond the Rugby World Cup in 2015, all underpinned by sound financial management.
"The Welsh rugby public, who have been so loyal to us all can look forward to the next four years with great anticipation."