Gannon made his debut last April and is ever-present in 2022, scoring a try against Wakefield Trinity last week in his 17th senior appearance.
“I am happy to be getting game time, getting plenty of minutes under my belt and learning every week,” Gannon said.
“That’s all I can really ask for, so I’m really happy.”
He insisted: “The last 18 months have been big for me.
“Leeds have given me that opportunity to play first-team rugby and be able to show what I can do.
“I am really grateful for that.
“The Rhinos have been everything I have always wanted in a club.
“They have given me the chance to play first team and I can’t thank them enough.”
Gannon is in the final year of studying for ‘A’ Levels, in maths, physics and business at Notre Dame in Leeds.
He said: “It has been a bit of a balancing act at times, but it has been a fairly smooth ride so far.
“My teachers have been great with setting work for me which has meant that I haven’t missed too much training.”
Coach Richard Agar described Gannon’s long-term deal as “great news” for Rhinos.
He said: “First and foremost, Morgan is an outstanding young man and a real credit to his family.
“On top of that he has a tremendous talent, which he has shown over the last 18 months. I am sure he will continue to progress over the coming years.”