Former Leeds United head coach Redfearn has been given a two-and-a-half-year deal at Rotherham.
The Englishman replaces Steve Evans, who left the Millers last month after more than three years in charge.
Well-known former Premier League referee Webb is a Rotherham fan, and he is delighted with the arrival of Redfearn at the AESSEAL New York Stadium.
Happy with the appointment of Neil Redfearn @OfficialRUFC; good luck Neil. Big shoes (& trousers!) to fill after Steve E was so successful— Howard Webb (@HowardMWebb) October 10, 2015
Rotherham are 21st in the Championship table at the moment with just eight points from 10 matches, level on points with third-from-bottom Bolton Wanderers.
Redfearn has a tough task at hand, and he will have to start picking up points sooner rather than later.
The 50-year-old parted company with Leeds at the end of last season after guiding the Whites to 15th in the Championship.