While the financial details of the deal were not disclosed by either club, Italian media reported that Everton would pay Napoli around three million euros in a loan fee and have agreed to a 22.5 million euro buy option for the 24-year-old.
The Denmark international joined Napoli from Bundesliga side Eintracht Frankfurt in 2023 and has made 29 appearances for the Italian club.
“Last year was a tough year for me but I’m so happy to be here now and I can’t wait to get started," Lindstrom told the club website.
"This is a season for me to come back on track. I think Everton is a very good fit for me and I’m ready to show why I should stay here."
Everton have also signed forward Iliman Ndiaye from Ligue 1 side Olympique de Marseille on a five-year contract. They kick off their league campaign at home against Brighton & Hove Albion on Saturday, August 17th.