Leeds have agreed an undisclosed fee with Scottish Rugby to bring the 18-year-old stand-off back to the sport – barely nine months after he left Castleford Tigers.
McLelland was England Under-18s captain before switching codes and, having quickly showed his class in the Edinburgh set-up, represented Scotland at the World Rugby Under-20s Championship earlier this year winning eight caps.
However, the Pontefract-born youngster has now moved back to Yorkshire in readiness to make his mark with Leeds in 2019.
The news is one positive for Rhinos although there was real disappointment last night after it was revealed legendary winger Ryan Hall has played his last game for the club.
The England star, who has scored 233 tries in 330 appearances for his hometown side, had a scan on his knee that showed he suffered a torn anterior cruciate ligament in Saturday’s win over Toulouse.
Hall, who is joining Sydney Roosters at the end of the season, will be ruled out for at last six months and Leeds director of rugby Kevin Sinfield said: “This is desperately disappointing news for Ryan first and foremost.
“I know how much he wanted to help the side during our Qualifiers campaign to make sure he finished his time at the club on the best possible note.
“He is a complete professional and I am sure he will fully recover from this set back.
“Our medical team will be in touch with the Roosters to ensure Ryan has the best possible support to get back to playing as soon as possible.”
McLelland, meanwhile, has started training with Leeds and signed a three-and-a-half year deal, but cannot feature this term after missing the transfer deadline. He said: “When you look around the stadium and speak to Kevin Sinfield about the plans for the team, I knew it was the right move for me.
“I’m looking forward to the opportunity of working with Rob Burrow as well. Rob was my hero growing up and I know there is so much I can learn from all the coaches here at the Rhinos.”
Qualifying through a grandfather born in East Ayrshire, Scottish Rugby paid a fee to recruit McLelland from Castleford after he turned down a new deal.
He played union until aged 13 before concentrating on league and Sinfield admitted: “We are delighted to have signed Callum.
“He was a huge loss to our sport when he left and it is great to welcome him back. He is an outstanding talent and there were a host of clubs who were chasing his signature.”
With current stand-off Joel Moon reportedly returning to the NRL, Leeds have recruited Tonga star Tui Lolohea from Wests Tigers for 2019.
Sinfield added: “Callum has a great football brain and will complement what we have next year in Richie Myler and Tui Lolohea. That internal competition is something I’ve been keen to improve.”
Meanwhile, Leeds prop Dom Crosby has received a two-game ban for a high tackle and use of a forearm against Toulouse.