He has signed a two-year contract at Wheldon Road, with an option for a further two years.
McLelland, 22, came through the junior ranks at his hometown club and earned England Academy honours.
However, he did not make a senior appearance before switching codes to join Edinburgh in 2017 where he went on to represent Scotland Under 20s on eight occasions.
McLelland moved back to rugby league with Rhinos in 2018 and made his long-awaited Super League debut the following season.
He made 16 appearances for them in total but never nailed down a regular spot.
McLelland now returns to Wheldon Road looking to push the likes of Jake Trueman, Danny Richardson and Gareth O’Brien for a place in Castleford’s creative hub as a new era begins under new coach Lee Radford in 2022.
He said: “I’m ecstatic.
“This is something that I’ve been speaking about for quite a long time – how I’d always like to come back – and it’s happened sooner than I would have thought but I’m glad for it.
“I played two minutes down the road at Lock Lane, always had a season ticket from being the age of about eight and stood in the Wheldon Road end singing all the songs.
“I always dreamed of playing for Cas’ and last time I was here I, unfortunately, didn’t end up playing a Super League game.
“But now I’m hoping to kick on and play here for the next couple of years.”
McLelland spent time on dual-registration with Featherstone Rovers while at Leeds, playing in the 2019 Million Pound Game, and has shown glimpses of his attacking quality when given the chance this term.
He has been blighted by injuries, however, having undergone ankle surgery at the end of last season and then, upon his return, requiring a groin operation.
McLelland had just got back into the Leeds side towards the end of the season when, in only his fifth appearance, he suffered a knee problem which also needed major surgery.
“I think I’ve become a lot more mature as a player,” he said, upon his return to Castleford.
“I’m a lot more patient. Loads of different tasks have been thrown at me on the field and off the field.
“I feel like I’ve matured a lot and hopefully that shows when I’m playing.
“I’m really looking forward to it; I’ve met Lee (Radford) a couple of times now and he seems a real good bloke.
“His record speaks for itself with the two Challenge Cups, and he's always been up there with Hull FC."
Radford said: “I’m delighted to welcome Callum back to the Tigers.
"He’s a young, energetic half-back who sadly this year has suffered a couple of injury setbacks.
“Alongside Danny Richardson, Gareth O’Brien, and Jake Trueman, he adds further competition to our halves.
“At just 22 as well, I’m thrilled to get a signing of his quality over the line, and he is a signing we have made with the future also in mind.
"I’m looking forward to coaching Callum."