Scott was part of the Millers side who memorably achieved back-to-back promotions during the Ronnie Moore era in the early noughties and joins up with former team-mates and now backroom team Paul Warne, Richie Barker and Mike Pollitt.
Surrey-born Scott, who is based in South Yorkshire, had been working as part of the recruitment team at Premier League side Watford.
Before switching to recruitment, the full-back, 45, who is the younger brother of former Millers chief Andy, enjoyed success on the managerial front in non-league circles with his ex-Rotherham team-mate Paul Hurst at Ilkeston, Boston United and Grimsby Town.
Scott replaces Jamie Johnson, who left the Millers at the end of February.
On his return to Rotherham, Scott, handed the position following an in-depth interview process, said: “It is a great opportunity to come into a club that I know and still have links to.
“I am really excited to get into the challenge of the job and to see where we can go with it.”
Scott will head up the club’s recruitment team which has also been boosted by the arrival of Middlesbrough’s former senior scout Chris Trotter.
Trotter said: “I am really excited to get into the challenge of the job and to see where we can go with it.
“It is a great opportunity for me, it is an exciting challenge to come in and work within a department which has great potential.
“It is a club I know well from working within football for a long time.
“I understand what the club is about and the type of players that we will be looking for.”