Derby president and chief executive Sam Rush said: “We enjoyed some fantastic and memorable moments under Steve during his previous tenure in charge.
“Steve’s arrival and subsequent work helped transform how we played our football.
“Steve’s time at Derby came to a premature end and I know he regrets that greatly. He values hugely his relationship with our supporters and I know that he will work very hard to ensure that the special connection returns.”
Pearson, who replaced Paul Clement as boss, was originally suspended by the Championship side pending a club investigation into his “behaviour” following a heated exchange with owner Mel Morris.
First-team coach Kevin Phillips and goalkeeping coach Pascal Zuberbuhler all remain part of the backroom team.
McClaren added: “I have a great affiliation with the club, having been here on three previous occasions, and I am really delighted at the prospect of finishing what we started.
“My ultimate aspiration remains exactly what it was before, to take Derby County back to the Premier League.
“This football club has fantastic ambition, brilliant supporters and wonderful backing from the chairman.”
But Derby lost 3-0 at home to Reading on the final day of the following season, meaning they missed out on the play-offs after ending February top of the table. McClaren was sacked in the same month.
BBC Radio 5 live’s Pat Murphy said: “McClaren was interviewed on Tuesday night just hours after Morris spoke warmly to a business leaders’ conference about the head coach he sacked almost 18 months ago after the club’s season had imploded.
“McClaren is recognised as one of England’s outstanding coaches. It is his fourth spell at Derby. His contract will run to summer 2018 and he’s expected to be in the dug-out for the Leeds match this Saturday. The rest of the coaching staff will be kept on.”
As well as coaching England from 2006-07, McClaren was previously manager at Middlesbrough, FC Twente, Wolfsburg and Nottingham Forest.
McClaren on his time with Derby
Speaking recently at an event at Manchester Metropolitan University, where he is studying for a masters degree in sporting directorship, McLaren told BBC Sport: “Many things were said about my time at Derby. I wanted to stay at Derby. Unfortunately the new owner came in, and I got sacked.
“If clubs can be run properly, people left to do their job, then the key is the owner and vision and policies and then working with good people, getting good players.”
Analysis – Derby’s McClaren U-turn a ‘shock’
BBC Radio Derby’s Owen Bradley
Shocked is an understatement considering the nature of Steve McClaren’s departure.
Though he was ultimately sacked, McClaren damaged lots of relationships at the club by never bringing to an end the links with Newcastle. In the eyes of some, that derailed Derby’s promotion campaign.
Mel Morris is a big fan of McClaren’s quality as a coach, but was part of the group that sacked him.
McClaren has acknowledged that there are plenty of people still upset by the nature of his departure. CEO Sam Rush mentions his regret and desire to rebuild his connection with the supporters. Entertaining football will do that.