The 58-year-old former Sheffield United boss has been quickly installed in the position following the sacking of Peter Taylor on Monday.
His first game in charge will be the away trip to Blackpool on Saturday 20th October.
Warnock has been out of football since resigning from the Blades job shortly after their relegation from the Premier League last season.
He will bring former England international Keith Curle in as his assistant. The future of the current coaching staff, including former Eagles player Kit Symons, is not yet clear.
Warnock will be expected to turn around a season that has started with the Eagles picking up just two wins from their first 10 league games.
It is understood he will be given the boost of a substantial transfer kitty in January to help him achieve promotion at the first attempt.