Kettings, 21, has penned a two-year deal with the Premier League outfit and will add depth to Tony Pulis' squad.
The Scotland youth international never played for Blackpool, but has featured in loan stints at League Two outfit Morecambe and Hyde in the Conference.
"I'm delighted because this is a massive club," Kettings told the club's official website.
"Everyone who I've spoken to about Crystal Palace has only had good things to say so I think it's a massive opportunity for myself and a good club to come to.
"I'm really looking forward to working with both [fellow goalkeepers] Julian Speroni and Wayne Hennessey as they'll both be able to teach me things and give me new perspectives."