The 35-year-old, who has had stints in Greece and South Africa following his release from West Ham last year, said the lure of English football was the deciding factor in him opting for a move to the Proact Stadium.
"I identify myself with English football because I've spent 14 years here," Boa Morte told the club's official website. "I like the crowds and the way that teams always play in a way that shows they are not afraid to concede."
The former Portugal international admitted he had limited knowledge of Chesterfield before joining, but a chat with former Fulham team-mate and current Spireites goalkeeping coach Mark Crossley had helped him make up his mind.
He added: "I bumped into Mark and we had a quick chat about me coming here. I didn't know much about the club so I made a few searches on the internet and then I decided to come. They've got a brand new stadium, good training facilities and Mark gave me some helpful information too."
Boa Morte, who has signed a short-term deal until the end of January, has spent most of his career in the English top flight with Arsenal, Southampton, Fulham and West Ham.