The 22-year-old flanker will make the switch from Leicester, although he has spent the past two seasons on a dual registration deal at Nottingham.
And having agreed a two-year deal at Headingley, Hemingway believes Leeds can bounce back to the Premiership at the first attempt.
He said: "I am really pleased to be joining Leeds Carnegie and I am excited about the potential we have here.
"It was a big decision for me to move away from Leicester having been part of the system there all my professional career but the vision here at Leeds Carnegie is something that I really want to buy into and I am looking forward to a fresh start here and the chance to get some game time under my belt next season.
"From my time at Nottingham, I know it is going to be a tough for us this season but the squad that Diccon Edwards is assembling looks to have a good balance to it and hopefully I can prove my worth during pre-season and stake a claim for the start of the season."
Hemingway follows Joe Ford (Northampton) and Stevie McColl (Doncaster) in joining Leeds.
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