The 26-year-old has signed a deal through to 2027 with the Blues, after Chelsea sealed a six-figure-deal for the defender.
Bjorn has been impressive for Everton in the Women's Super League so far this season and will provide a much-needed option at the back for Chelsea, with Jess Carter at times having to fill in at centre-back due to Millie Bright's injury issues.
With 57 international caps to her name already for Sweden, Bjorn will bring plenty of experience as well as versatility to Emma Hayes' side, having played across the defence and in the centre of midfield too.
"You will see that I will fight 100%, I want to win every duel and every game," Bjorn told Chelsea's official website as her move was made official.
"You will see some of my qualities with my passing and passing through lines is my biggest quality, I would say. I hope that I can help the team with my style of play."
Chelsea's first match back after the winter break is at home to West Ham in the FA Cup this weekend, before the focus shifts to games against Manchester United and Real Madrid at Stamford Bridge.
Bjorn added: "It’s an amazing stadium, it’s a really nice stadium. It’s an amazing pitch and I cannot wait to get started and play in these big games.
"I want to help the team as much as possible and I want to win as much as possible. I’m ready to get this journey started."
