Mellor makes the move from Leeds Rhinos to Wheldon Road immediately and will be in contention for Radford’s side straight away, including for this Sunday’s Betfred Super League home game against Catalans Dragons.
The 27-year-old will wear the number 37 shirt in 2022 and will be sponsored by Aysgarth Rooms.
“Alex is a really athletic, strike ball player on an edge," said head coach Radford.
"I’ve watched him over the years and been impressed with him and he’s probably not struck the chords that he wanted to so far this year. I think we’re picking up someone who we can try to get back into the swing of things and enjoying his rugby again.
“He has been on the cusp of the England Knights selection, he’s of the age where his best years are still in front of him and I think he will be a good coup for us.
"I got a really good feeling for him and everyone I’ve spoken to, player and coach, has only had good things to say about him in how he trains and approaches training.
“Competition is what we need and he will be playing on an edge. This time of year to pick someone up of his quality is fantastic, as is having him long-term too. Hopefully, this place will be good for him as he will be good for us.”
Born in Halifax, Mellor began his rugby league journey with amateur club King Cross Park, he then joined the youth side at Bradford Bulls where he emerged as a talent, making his top-flight debut in 2013 and playing first team rugby at Odsal for four years.
Following the Bulls’ liquidation in early 2017, he signed for Huddersfield Giants where he played for three seasons before making the move to Leeds from the 2020 season, lifting the Challenge Cup trophy at Wembley in his first year with the Rhinos.
On his move to Castleford, Mellor said: “It feels good, it’s been a bit of a long process getting things sorted, so to finally have it all figured out is a good feeling.
“Back-row suits my play style, I think I’m a bloke who is going to put his head down and work hard for you, come up with some plays when I need to but put the team first and do every little thing I can to make the team better.
“It’s good to be a part of it, you look at some of the signings that we’ve made and the prospects we’ve got for next year, it is really exciting. It is not one of those places that you come and aim for mid-table, this is one of those places where we want to be up the table and push.
"Looking at the signings and the squad we’re building, it’s definitely something we can do.
“Lee Radford is a big reason, I sat down with him the first time and felt comfortable around him and liked what he had to say, his persona, how he viewed things in rugby. I think the first time we met it wasn’t too formal and we get on, I could really see myself playing under him and coming to Castleford to see what we can do.”
It has been a tough year due to injuries for Mellor, but he looks to be back to 100 per cent and outlined his initial goals with the Tigers:
“To cement myself in the team is definitely one, but I want to kick on and hopefully find some play-off football this year and find some form again.
"I feel like the last eight/10 months have been a bit of a struggle for me playing-wise, I got a really bad injury and it sort of set me back. I’ve been in and out injured so for me it is about finding a bit of consistency in my playing time, hopefully staying injury-free and kicking on with Cas to see what we can do.”
Mellor is looking forward to playing in front of the Cas fans at the Mend-A-Hose Jungle as a home player.
He added: “It’s going to be different! You come and play Cas and the pitch is real enclosed and the fans are on top, when they get at you, they get at you, we played here last year and I played outside Luke Gale. He got hammered the whole game, the fans actually made me laugh on the field, which is mad!
“It’s going to be nice to have that feeling where all the fans are behind you and supporting you, that wave of noise motivates you on and I’m looking forward to that carnival sort of atmosphere, it’s going to be good.”