Diamond was appointed in a rugby consultancy role at Sixways in November, and he will remain in that capacity for the remainder of this campaign, while also immediately taking charge of Worcester’s rugby programme.
Solomons, meanwhile, will retire from coaching at the end of June.
Worcester co-owners Colin Goldring and Jason Whittingham said: “Having taken the time to work with Steve in his role as a lead rugby consultant, it was the logical decision to offer him the role as director of rugby for the next two seasons.
“Steve is an experienced and proven director of rugby with the qualities needed to take the club to the next level and achieve our ambitions of competing at the top end of the Premiership.
“We have invested a great deal into ensuring we have all the right ingredients for the club to reach its full potential.”
On Thomas’ departure, they added: “Jonathan has given his all to the club. We appreciate everything he has done in his time at Warriors, both as a player and a coach, and we wish him all the very best in his future ventures.”
Diamond enjoyed a successful spell with Sale, gaining Heineken Champions Cup qualification on five occasions and winning the Premiership Rugby Cup.
“We have a really exciting challenge in front of us, and it is one that I am relishing,” he said.
“We have enthusiastic owners who have ambitions for the club to be established in the top six of the Gallagher Premiership and playing in the Heineken Champions Cup.
“Clearly, we are not where we would like to be at the moment as a club. To achieve our ambitions, our results need to improve and changes need to be made.
“A key part of my role will be the recruitment of players and staff. Worcester is a hot-bed of rugby with a fantastic core group of supporters. We want to grow that supporter base and give the city, county and region a successful and sustainable Premiership club that everyone can be proud of.”
Worcester are currently 12th in the Premiership, having won three of their first 12 games. They host Northampton on Saturday.
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