Doyley has been on trial with the Millers having been without a club since leaving Watford in the summer and played 90 minutes in the reserves on Tuesday before earning a short-term contract on Thursday.
Warnock had no hesitation in getting the 33-year-old fixed up after he tried to sign him at QPR earlier in the season.
"I wanted to sign him at QPR but I wasn't allowed to at the
time," the Millers boss said.
"He kept in touch and when I came here I made contact with him and he came
straight up.
"He's such a good pro. He doesn't put himself in the limelight,
he's not one of those lads, and I think that's why he hasn't got fixed up.
"He
was an absolute hero at Watford. He's a super lad who can play anywhere across
the back four.
"It's not like taking a loan player from the Premier League where
we're not really sure. I know exactly what he's going to give us."
Doyley becomes the third experienced free agent to join the Millers this week following the arrivals of Jerome Thomas and Paddy Kenny and the sixth this season following earlier signings of Leon Best, Stephen Kelly and Luciano Becchio.
