Until recently, the ex-Warrington Wolves star had been playing with Wakefield Trinity but he will now follow club captain Danny Kirmond to York for next term.
Atkins, 34, has made more than 300 top-flight appearances and, with 186 tries, is Super League’s fifth-highest all-time try-scorer.
He has played in Grand Finals with Warrington and also won the Challenge Cup with them in 2010 and again two years later, scoring in both of those Wembley appearances.
With four tries in eight Test matches for England, Atkins’ pedigree is undoubted and his experience will be crucial for James Ford’s side.
“Ryan is a big signing for us and I’m sure the supporters will be excited to watch him impose his physicality on our opponents,” said Ford, about the Leeds-born player who started his career at Bradford Bulls before initially joining Trinity in 2006.
“His track record speaks for itself – but I’m excited to work with someone who I feel will help lift standards on and off the field.
“We see Ryan as a leader and we’ll be expecting him to lead us right from the front.
“He’s been around some elite environments and I’m confident he will have a huge impact on us in 2021 and beyond.”
Atkins rejoined Wakefield from Warrington on loan until the end of the season last August, playing just one match - the final day relegation decider against London Broncos - before moving permanently for 2020.
He featured with Chris Chester’s side four times at the start of this season, scoring two tries, but has not been involved since the return from lockdown.
He expects 2021 to be the final season of his career and - as he prepares for life as a part-time player - already has plans to go into recruitment consultancy.
However, firstly, Atkins hopes to help York, who will play next year in their new purpose-built stadium and already have the likes of Danny Washbrook and Chris Clarkson in their ranks, make a bid for Super League.
He is looking forward to working with Ford and said: “I spoke to him and I could just tell straight away that his passion and hunger for the game was evident.
“His philosophies and approach reminded me of Tony Smith and under him at Warrington was when I played my best rugby so I just knew I would be able to work really well with Fordy.
“I’m really excited to do this and I’ve not been excited for a while.
“Any good team needs experience and knowledge of the game and I’ll be trying to pass that on in training as much as I can.
“I want to help develop the club’s culture with the players, make that a winning culture and make winning a habit.
“I want to help York City Knights get promoted into Super League, where I feel they’re capable of playing and, with the facilities, it’s where they deserve to be.”
Support The Yorkshire Post and become a subscriber today.
Your subscription will help us to continue to bring quality news to the people of Yorkshire. In return, you’ll see fewer ads on site, get free access to our app and receive exclusive members-only offers.
So, please - if you can - pay for our work. Just £5 per month is the starting point. If you think that which we are trying to achieve is worth more, you can pay us what you think we are worth. By doing so, you will be investing in something that is becoming increasingly rare. Independent journalism that cares less about right and left and more about right and wrong. Journalism you can trust.