Spellman, a product of the well-acclaimed Park View Academy in the North East, has agreed a temporary deal on a youth loan.
The exciting teenager impressed during a trial period at the Academy of Light in the 2021/22 season and was signed on a permanent basis this summer, joining up with Mike Dodds and Michael Proctor's Sunderland Under-21 side.
The 19-year-old also made his first team debut for the Black Cats in their Carabao Cup tie at Sheffield Wednesday in August.
Whitby Town manager, Nathan Haslam, said: "He made his debut for the Sunderland first team a couple of weeks ago.
"He's a young boy with lots of potential and lots of pace. He's very direct and he's going to be an asset to us without a doubt.
"I think it's a thing that works for both clubs. For Sunderland it's good to get one of their young players into playing men's football, and for us it's about bringing in quality.
"He's in for an initial month and we're going to make as much use of him as we physically can."