The Aviva Premiership club confirmed the former Wasps coach will join the coaching team following the news Toby Booth, Justin Bishop and Neal Hatley are to leave the club.
Edwards will continue in his role as Wales defence coach, but spend one day a week at the Aviva Premiership side as allowed under his contract, it was reported in the Guardian.
Edwards was a key member of the Wasps coaching team when the club won Premiership titles in 2003, 2004 and 2005 and the Heineken Cup in 2004 and 2007.
He joined Wales as defence coach under Warren Gatland in 2008, helping them win the Six Nations Grand Slam in 2008 and 2012.
The former Great Britain rugby league international told the Exile's official website: "I'm excited at the opportunity of being involved in a Premiership club set up again.
"London Irish has some fantastic players who I am looking forward to working with. The squad has put in some great performances this season and have been unlucky not to come away with more wins. I want to work with the team to see how we can then turn those frustrating last-minute defeats into victories."
Irish director of rugby Brian Smith will also take on a more hands-on coaching role to run the team's attack, the club revealed.
Smith said: "Shaun is a world-class coach and he has been responsible for introducing a defensive system that has changed the shape of the modern game, consistently producing watertight defences in the Premiership, Six Nations, Lion's tours and Rugby World Cups. He is a tough, hard-nosed coach, who I am confident will, alongside me, help to bring out the very best in the London Irish squad.
"We will have a strategy in place for next season to slash the numbers of points we concede in the Aviva Premiership. If we can do that then, this time next year, we can be a top four team and two games away from silverware."
Irish also confirmed they are looking to announce the appointment of a new forwards coach shortly.
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