The free-kick specialist started his career as a trainee at Rangers in May 2004 before being loaned to Ross County in 2004 and St Mirren in 2005.
"I am absolutely delighted to have signed Charlie," manager Ian Holloway told the club website.
He added: "He played a massive part in keeping the club in the division.
"Having watched all the DVDs from last season and listened to the staff and supporters, I know exactly what he can bring to the club.
"I would like to thank [club president Valery] Mr Belokon for making this transfer happen. He has put an unbelievable amount of trust and faith in me and I am extremely grateful, I am sure he will be delighted as all the supporters and I am at signing Charlie."
Adam scored 18 goals in 86 appearances for Rangers and is expected to go straight into Blackpool's starting line-up for Saturday's Championship opener against QPR.