Orr made more than 200 appearances as a player in two spells for the Tigers from 1997-2003 and 2011-12 and joined the coaching staff in 2013, initially as assistant to Ian Millward.
He then had a brief spell as head coach before the arrival of Daryl Powell later that year.
Orr said: “It’s been a very tough decision to make but one I feel that I have to do at this stage of my coaching career.”
Powell said: “Danny has been a phenomenal servant for Castleford Tigers as a player and as a coach and has been a massive support to me over the last seven years in my time at the club.
“Danny will be with us for the remainder of this season and I know he will continue to help drive our standards of performance.
“I respect his decision to want to advance his coaching career as we move into 2021 and I wish him all the best.”
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