Tarkowski has signed a four-year contract at Goodison Park after leaving Burnley following their relegation to the championship.
Tarkowski's contract with the Clarets expired last month and he was keen to explore a new challenge.
The 29-year-old spent six-and-a-half years at Burnley after joining from Brentford in January 2016, going on to make 194 Premier League appearances at Turf Moor.
The two-time England international has expressed his delight at securing his next career move.
Speaking to the Toffees' official website, he said: "I'm excited to have joined Everton. It's a massive club. I'm really looking forward to the years ahead and I'm thankful for the opportunity that I've been given.
"Speaking to the manager, it was very important to see what he wants from his players and his team, what he saw in me and why he wanted to sign me. Speaking to [Director of Football] Kevin Thelwell was also a factor. They both spoke about the ambition here which was really important for me.
"I'm an ambitious person, I want to achieve, I want to win things and I've come here to be successful.
"And then there are the Everton fans. The support they gave the team last season was incredible. You saw just how big the fanbase is. Despite a difficult season, Everton fans got behind their team more than ever.
"I think they are a massive factor about this club. Hopefully, successful times are ahead and, with the talent we have in the squad, we can give the fans something they really enjoy."
