The 22-year-old joins from the eight-time Barclays Women's Super League champions, having previously spent time on loan at Crystal Palace Women, Brighton & Hove Albion Women and Charlton Athletic Women.
During her time with the Seagulls, she went on to make 23 appearances before an injury would cut short her time there.
Jorja made her WSL debut aged 17 for Chelsea, coming on as a substitute in a win against Aston Villa Women. In the following season, she would also appear in the UEFA Women's Champions League.
Internationally, the defender has represented England up to under-23s level.
On signing for Newcastle United Women, Fox said: "I'm really excited. I've spoken to a lot of people about the club, and everyone seems excited about the project, and I can't wait to get started.
"We're competing for promotion, and that's the main goal. There will be tough moments and good moments because this league is tough."
Manager Becky Langley said: "Jorja joins us with a lot of potential, and we are looking forward to helping her reach that.
"She brings quality to both the attacking and defensive side of the game. She has a real desire to connect the play moving forward and dominates in her one v one defensive actions."
This signing is subject to FA clearance.
