The Warriors' Aviva Premiership rivals Wasps confirmed earlier in the day that former Wales full-back Howarth would be leaving them after one season at Adams Park.
And 44-year-old Howarth will now head to Sixways, where he will work with recently-appointed rugby director Dean Ryan.
"I am naturally delighted that Shane will be joining us at Warriors," Ryan said.
"Shane coaches players to have a real ambition to play, and you only have to look at the back-line development he has achieved this season at Wasps to see his pedigree.
"He also has the ability to develop, support and bring through youngsters, and that is crucial to the way I want Warriors to operate.
"Shane has a strong coaching background around the world, with Super 15 and international experience, and he will be a big asset to the coaching set-up at Warriors."
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