Hoadley has been with the Adams Park club since 2004 after joining from London Irish prior to the end of his playing career, and has spent the last three seasons working as a coaching assistant.
Hoadley has been acting as Wasps' defence coach for the last six months while former head coach Shaun Edwards was working with Wales, and he now steps up to the roll full time following Edwards' recent decision to leave his post.
Wasps rugby director Dai Young said: "Rob has been doing an excellent job working with our defence in recent months and it's fantastic to be able to promote someone from within.
"He knows the club through and through and with his experience as a Premiership player he has been able to transition from player to coach very easily."
Hoadley added: "While we were all sad to see Shaun Edwards leave, I have been privileged to learn huge amounts by working closely with him in recent years.
"Hopefully I can pass on some of his great experience to a largely new squad at Wasps on the road to renewed success for the club."
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