The 28-year-old has secured a four-year deal, tieing him to Everton until June 2026.
Tarkowski, who has two England caps, becomes Frank Lampard's first signing of the transfer window, as the Everton manager looks to improve on a squad that finished 16th last season.
Defence was a major area of concern under Lampard and his predecessor Rafael Benitez, with Ben Godfrey and Yerry Mina suffering injury-hit campaigns. Indeed, Everton conceded 66 goals in the 2021-2022 season, the 16th-worst total in the Premier League.
While Tarkowski was unable to help Burnley retain its top-flight status, the centre-back had a strong individual campaign.
No defender in the league competed for (217) or won more aerial duels (153) than Tarkowski.
Brentford's Pontus Jansson, with 186, was the only defender to make more clearances than Tarkowski's 183, while Everton's new addition also ranked second for headed clearances (101).
"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," Tarkowski said.
"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.
"I'm an ambitious person, I want to achieve, I want to win things and I've come here to be successful."
While it has strengthened in defence, Everton's financial issues have resulted in the sale of star forward Richarlison, whose move to Tottenham Hotspur went through for a reported £50 million ($88.1 million) fee, with add-ons taking the deal potentially up to £60 million ($105.8 million).
The Toffees have been linked with Spurs midfielder Harry Winks, while reports of interest in Jesse Lingard, who is another free agent after he left Manchester United, have also emerged.