The 35-year-old, who was released by the Pools at the end of last season, had been on trial with Chesterfield since the beginning of the month.
"I'm really excited at the prospect of a fresh challenge," Humphreys told Chesterfield's official website.
"I've been so impressed with the players, management team and facilities at the club and I can't wait to get started. This is a fantastic football club and I can't wait to get started."
Humphreys spent 12 years with Hartlepool, making over 500 appearances in the process.