Ellis had been the assistant at Turf Moor since 1998, following Ternent from Bury to Burnley.
A couple of seasons ago Ternent had a 'disagreement' with Blackwell at Bramall Lane, during half-time, when Ternent accused the then
After failing to get former Walsall manager Colin Lee, Blackwell turned to Ellis, who has previously managed Blackpool, Bury and Lincoln City.
Blackwell said: "I have known Sam for a long time and even played for him when I was a teenager. He is well respected in the game because he has been working in the First Division for a number of years and has been instrumental in Burnley's rise through the leagues. He knows what is needed at both ends of the table, has good contacts and a great deal of knowledge and understanding of what is required. I am delighted to have been able to bring him in and I am looking forward to working with him."