The 26-year-old, Chelsea’s first signing of the January transfer window, has agreed a contract until 2027.
Bjorn has 61 caps for Sweden, helping them win a silver medal at the 2020 Tokyo Olympics and finish third at the 2019 and 2023 Women’s World Cups.
“To sign for one of the biggest clubs in Europe feels like part of a dream you have when you are young,” she said.
“It feels amazing. I’m very excited to get this journey started.”
Chelsea general manager Paul Green said: ‘Nathalie is a very experienced, versatile player that we have been tracking for a long time.
“She is a leader, has good pace, is good on the ball, and knows our league very well.”
Bjorn, who can also play in central midfield, scored two goals in 44 WSL games for Everton after joining from Swedish side FC Rosengard in 2021.
Chelsea are three points clear at the top of the table after 10 games this season.
