Howarth, who has been with Wasps for one season, has decided to move out of London for family reasons.
Former Bath skills coach Brad Davis will arrive at Wasps this summer as an assistant, working on defence, with current Wasps fly-half Stephen Jones taking charge of attack.
"We are sorry to lose Shane," Wasps rugby director Dai Young said. "He has done a good job for us this season, and we've reluctantly released him from his contract after his requests, due to his family wanting to move out of London."
Jones, Wales' most-capped player, now steps into the coaching arena after announcing his retirement from playing earlier this term.
"Stephen has already had a big influence in our attack this season, and I am very confident in his ability to step up and carry on where Shane has left off," Young added.
"Brad Davis will also be a very good addition for us. He is an excellent coach and is highly-rated by the players who have worked with him. I think he brings a nice balance to the coaching team, giving us a much stronger focus on our defence."
Former rugby league player Davis said: "I am excited to have the opportunity to join Wasps and to work with Dai and the team in helping them to achieve their goals.
"It is a squad full of huge potential and they have played some great attacking rugby this season, so I am really looking forward to working with the players to strengthen their defence so that we can compete and win games consistently at the highest level."
Wasps have also announced the signing of back-row forward Guy Thompson from Championship club Jersey.