The 21-year-old joined the Ladbrokes Challenge Cup holders in the winter from Kingstone Press Championship side Halifax on a 12-month deal and made his Betfred Super League debut against Leigh Centurions in May.
Rawsthorne is currently on loan with Leigh and has also spent time at League 1 clubs York City Knights and Doncaster but remains in the long-term plans of Hull coach Lee Radford.
BREAKING NEWS: @NickRawsthorne has signed a two-year extension with Hull FC! See more below!https://t.co/MVg43PZsfB pic.twitter.com/YLrrZ83fyY
— Hull FC (@hullfcofficial) June 29, 2017
"I am really pleased to have extended Nick's contract," Radford said. "It is great news for us.
"The coaching staff have been really impressed with his development this season and we are looking forward to that continuing with us over the next couple of years."
