The Portuguese teenager has joined the Toffees on a four-year contract.
Chermiti is Everton's third summer signing, joining Ashley Young and Arnaut Danjuma in moving to Goodison Park for the start of the 2023/2024 season.
The 19-year-old came through Sporting Lisbon's youth system and made his first team debut in January this year, going on to make 22 appearances in all competitions and scoring three goals.
"It's a big move for me. Joining Everton is a new beginning, a new page and I'm very happy to be here. It is a beautiful city and a beautiful club," he told the club's official website.
"I'm looking forward to meeting the fans, my new teammates and to get to work with the coach. I want to embrace everything about the club.
"I have new goals now. I'm here and I want to do my best for Everton. I want to help the team. I hope the fans will like me and I want to show them what I am capable of.
"Everton is a big club. A lot of legends have played here. I couldn't turn down this opportunity. It's a big moment for me and now I'm fully focused to get to work.
"I am a hard-working player. I have pace and I think I have good finishing ability. I'm very happy to be here and I hope to keep improving with Everton.
"It will be a dream to play at Goodison Park. I hope to play a lot of games at Goodison and I am very excited for the beginning of my journey at this club."
Everton manager Sean Dyche added: "Youssef is a talented young striker who can add a different dimension to our squad.
"He is still a teenager who is learning his game, which we will be mindful of, but we think he has the raw talent and ingredients to be a very good player and that's why we are pleased to have signed him for Everton."
Everton will host Fulham in their first Premier League game of the 2023/2024 season on Saturday.
