Billy Davies said he was "delighted to bits" to be taking over as Derby boss but warned of tough times ahead.
Davies took over as Preston boss in August 2004
Davies was unveiled as Terry Westley's replacement after Derby agreed a compensation package with Preston.
He said: "I see this as a wonderful opportunity and I'm looking forward to getting my teeth into this club.
"But we have a big job on our hands and we have to build and make progress slowly and take the club forward by very small steps."
The new Rams' boss added: "There are a lot of good players at this club and I have to get them playing to their maximum potential.
"I'll also look to bring in one or two new faces," said Davies who would not be drawn into whether he would be returning to raid his former club Preston.
Preston chairman Derek Shaw cleared the decks for Davies to speak to the Rams after agreeing a compensation package for the highly-rated Scot.
Under the terms of the package Preston will receive almost two years of Davies' wages in compensation.
Shaw told Preston's website: "We took the decision that the deal would be in the best interests of the club, and granted Billy permission to talk."
Referring to his departure from Deepdale, Davies added: "There will be some people at Preston who will be sorry to see me go, and some who will be happy."
And Davies insisted that the move was not a step down in his career.
He added: "I felt it was time for a change and time for a new challenge and there is no bigger challenge in the game at the moment than Derby County.
"It's a massive job and I am delighted to be manager of this tremendous club.
"It's not a step down. I've moved to another Championship club, one with passion, ambition and potential in abundance, and it's up to me to harness that now."
Former Motherwell boss Davies had been in charge at Deepdale since taking over from former Scotland manager Craig Brown in August 2004.
He showed his mettle by guiding the Lillywhites to the Championship play-offs in successive seasons.
Davies was recently interviewed for the manager's position at Charlton, which has now been filled by Iain Dowie.