The 25-year-old has been with Carlisle since 2008, making 160 appearances for the club and turned down a new deal to join the Saddlers.
"We knew he was after a new challenge. He can come in and be a dominant number one for us," Walsall manager Jon Whitney told the club website.
Meanwhile, 22-year-old goalkeeper Liam Roberts has agreed a new one-year deal.
The contract signed by former Chester loanee Roberts, who has made one senior appearance for Walsall, includes the option of a further year in the League One club's favour.
Find all the latest football transfers on our dedicated page.
Walsall have signed goalkeeper Mark Gillespie on a two-year contract from Carlisle United on a free transfer.