He has agreed a three-year deal at Wheldon Road and is a direct replacement for former Man of Steel Luke Gale, who was recently sold to Leeds Rhinos.
The talented Richardson, 23, earned Super League Dream Team selection with Saints in 2018. However, he made just 13 appearances this term after losing his place to Theo Fages and largely had to watch on from the sidelines as Saints raced to the League Leaders’ Shield and won the Grand Final as well as reaching Wembley.
“There were a few clubs enquiring about me for next year,” said Richardson. “But the minute my agent came to me and told me about Cas being interested I jumped at the chance and couldn’t wait to get the deal over the line.
“With the coaching staff we have and the way other half-backs have developed while they’ve been at the club over the years, I thought that if there was a place for me to improve and get the best out of myself it was going to be with the Tigers.
“From a personal point of view, it’s been an awful year for me and I’m looking forward to reminding people what I can do and putting myself back on show.
“I feel like I’m a good talker who can steer the ship and if I can do that then hopefully I’ll be bringing the best out of the team at the same time.”
In an exciting partnership, Richardson is set to link up with Jake Trueman, the 20-year-old who won the Super League Young Player of the Year 12 months ago.
Trueman also played for England Nines in Sydney this morning ahead of Great Britain duty in New Zealand and Papua New Guinea while Richardson is in the Knights squad to face Jamaica at Headingley on Sunday.
Castleford head coach Daryl Powell added: “We have just made a signing that should excite and engage all of our supporters as we look towards 2020.
“To work alongside Jake Trueman, we have signed one of the best young half-backs in rugby league.
“Danny is a player of real quality with the potential to play international rugby.
“He has a sharp rugby mind alongside his ability to kick the ball in a special way both for goal and tactically.
“We are looking forward to helping Danny go to the next level in his career and can’t wait to get started towards next season.”