The former Tottenham Hotspur, West Ham United, Portsmouth, Southampton and Queens Park Rangers manager will assist Head Coach Darren Wassall and the rest of the Rams coaching staff who are in post until the end of the season when a full review will be undertaken.
Redknapp, 69, has signed a contract for the rest of the current campaign and brings with him extensive experience across the English game.
After a successful playing career he moved into management on the South Coast with AFC Bournemouth in 1983. He spent seven years at West Ham United before moving to Portsmouth, where he had two spells in charge, including winning the FA Cup in 2008.
During his time at Tottenham, Redknapp was named the Premier League Manager of the Year for the 2009/10 campaign and also guided the North London club to the Champions League quarter-finals.
The most memorable part of his three-year tenure at Queens Park Rangers was securing promotion to the Premier League via the play-off final of 2014.
Derby County Chairman Mel Morris said: “It is excellent news that Harry has agreed to join us. His experience spans over several decades and he is one of the most knowledgeable and informed figures in the game.
“When I spoke with Harry about the possibility of helping out on a short-term basis, it was evident from the start that he was excited at the prospect of joining us. I am sure he willperfectly complement Darren and the rest of our staff.”
Derby County’s President & Chief Executive Sam Rush added: “As we move into the closing stages of the season, we feel that Harry’s know-how will be valuable to us. He brings a high level of awareness and understanding of the Championship promotion race.”
Harry Redknapp said: “From the first conversation I had with the Chairman it was clear he has exciting plans for the football club. I am delighted to be able to help out and am looking forward to working with Darren and his team.”
Darren Wassall said: “This is a great opportunity for me and the rest of the coaches to work with somebody of Harry’s experience for the remainder of the season.”