The 30-year-old has previously represented Arsenal, Bristol City, Birmingham City, Manchester City and, most recently, Liverpool, where she left last month.
Lawley joins the Toffees with 132 WSL appearances to her name. 
In her first evertontv interview, she said: “I’m really excited for the next challenge in my career. I’ve spent five years in Merseyside and I’m excited to now be a Blue.
“I fell in love with the people, with the fans. Every time I played against Everton, the fans were amazing, even if they gave me a bit of stick.
“I’m excited to now be on their side and helping Everton to become successful.”
Lawley becomes Everton's fourth signing of the summer transfer window.