The American central defender will join the Rams and new manager Steve McClaren on a three-month loan from Leicester City.
Whitbread played four games in all competitions with Leicester City this season, and he scored a goal against Derby County last season. The Texas-born 29-year-old is eligible for Tuesday's match against Ipswich Town after training with his new side on Monday.
Whitbread, who came up in the Liverpool youth system and also played for Millwall and Norwich City, has battled numerous injuries throughout his career and has yet to earn a cap with the full U.S. national team. He represented his birth country at the U-20 and U-23 level and was called in for a pair of friendlies by then-U.S. manager Bob Bradley in March 2011, but he had to withdraw because of an injury.
Derby County, which currently employs on-loan D.C. United forward Conor Doyle, announced that former manager Steve McClaren would be taking the reins for the ousted Nigel Clough on Monday as well.