Redfearn managed just one victory from his last eight matches in charge of Rotherham, leaving the club in the relegation zone.
Warnock's most recent managerial gig was as caretaker coach of QPR earlier this season.
BREAKING: Neil Warnock has agreed a deal until the end of the season. #rufcpic.twitter.com/mGphHxqbLb
— Rotherham United (@OfficialRUFC) February 11, 2016