The 27-year-old, who turned in a man-of-the-match display in Ireland's 16-11 win over Italy last week, joined Wasps from Munster in 2005 and in his first season he overtook Matt Dawson's as Wasps' first choice number 9, was capped by Ireland and collected a Powergen Cup winners' medal.
With club and country, Reddan has gone from strength to strength over the past two seasons. He scored the opening try in Wasps' Heineken Cup final win over Leicester Tigers last May and by the end of the World Cup he had displaced Peter Stringer as Ireland's starting scrum half.
Commenting on the new deal, Reddan said: "I am very happy with this decision. Since joining Wasps, the club very quickly became a home away from home for me, and there is something very special about the place that means I am delighted to be staying on for a further two seasons.
"I've learned a lot in the last two-and-a-half years at Wasps and I do feel there is more to come, both in what I can learn and in what the team can achieve. Wasps have been very successful in recent years, but we remain ambitious to build on that success this season and in the future.
"Wasps is a great club, with top class players all over the park, and providing we work hard as a squad and keep our winning mentality, we can fulfil our aim of continuing to win trophies."
Wasps director of rugby Ian McGeechan said: "We are delighted that Eoin has committed to Wasps for another two seasons. He has become a very important part of what we do and how we do it - his all-round game suits the way we play and the speed and quality of his passing has become a key factor in our approach to games.
"His game has come on hugely in his time with the club and he has become a very influential player, one that both Shaun Edwards and I enjoy working with.
"Shaun and I are delighted to see Eoin's progress being rewarded at international level. Wasps' ethos is firmly based on providing the best support and coaching for our players, giving them a platform to realise their ambitions to play at the highest level.
"Eoin's decision to extend his commitment to Wasps is affirmation that we are delivering on that front, as well as a tremendous fillip to the club."