The striker will join the Premier League side at the start of next season after agreeing the move.
Norwich manager Chris Hughton said: "Ricky's profile is a perfect fit for us. He's young, ambitious and a proven goalscorer.
"He has an excellent goalscoring pedigree and he's a young man very keen to continue his personal progression and to play in England. He's already an exciting talent but he still has more development as a player ahead of him.
"I'm delighted we've been able to agree a deal with Sporting Lisbon and with Ricky and we look forward to welcoming him to the squad in July, once all of the paperwork gets sorted out."