The 51-year-old will join boss Steve Evans, assistant Paul Raynor, goalkeeping coach Andy Dibble and fitness coach Paul Warne in the Millers' dugout after he left his position at Wigan, where he was enjoying a second spell.
Black, a former player with Aberdeen and Metz, has close to 20 years of coaching experience and during that time enjoyed a lengthy relationship with Steve Bruce, assisting him at Birmingham, Wigan and Sunderland.
Black's arrival at New York Stadium ends a lengthy search for Evans, who has been keen to add to his backroom staff for some time.
The Millers boss was delighted to get a figure with such pedigree to join the club.
"I became aware that there was a possibility that Eric might leave Wigan and after making contact, I am delighted having met him that we managed to put something together,” Evans said.
“Eric is fundamentally a coach who arrives here with impeccable references given to me by the likes of Craig Brown, Steve Bruce and Gerard Houllier.
"He has a wealth of experience and knowledge as a coach from a career spanning over 20 years and he will have a major part to play at Rotherham United going forward.Steve Evans on Black appointment: "Eric is fundamentally a coach who arrives here with impeccable references." #rufc— Rotherham United (@OfficialRUFC) July 8, 2015
“His CV as a player and a coach is of the highest quality and he is someone I have known and respected for almost 25 years.
“Paul Raynor and Eric are already vey much working in tandem and the lads have already stated they are delighted with how the backroom team is now working.
"Eric has brought a new voice to the training ground, and we will benefit greatly from his expertise as we look to build on our success of the last three years.”
The Millers have also announced the return of Mike Preston as the club's head of medical following the retirement of Denis Circuit.
