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.

They failed to score a point in the second half as Rob Elloway, Matt Evans and Joe Atkinson were yellow-carded.
"The communication was there, we just weren't reacting to what he (the referee) was saying," Davies said.
"The cumulation caught up with us with three yellow cards - you don't often see that, but they were justified."
Pirates had beaten their Championship rivals in all three of their previous meetings this season.
Evans and on-loan Exeter scrum-half Stu Townsend scored tries for the Cornish side, who will lose head coach Davies in the summer due to budget constraints.
"In that first half that's all that was keeping them in the game, our ill-discipline," he told BBC Radio Cornwall.
"Ill-discipline came back to haunt us - it was one bridge too far.
"There have been some dark days and some long days, so to get to a final would've been great, but we haven't achieved that."

Christopher Clarke, 29, contacted girls, aged 15 and 16 at the time, via Facebook, Snapchat and Twitter.
He also bought the Ysgol Bro Dinefwr pupils gifts including T-shirts, earrings, sweets and games consoles.
An Education Workforce Council hearing concluded his actions amounted to professional misconduct.
One girl told how Mr Clarke sent her a message saying: "I kept having the same thought over and over again. How much I wanted to grab you, kiss you..."
The girl, now 19, said he also invited her to one-on-one sessions in his chemistry office and told her not to show anyone the gifts her gave her.
Another girl, now 17, said his actions made her feel uncomfortable and he was "acting in a creepy nature".
A third student said she told Mr Clarke she thought his messages were inappropriate and he later asked her to delete their conversation.
Police investigated but no charges were brought against Mr Clarke.
The school also began an investigation but he resigned before any findings were made.
Education Workforce Council chairman, Steve Powell, said Mr Clarke's conduct "clearly breached boundaries between teachers and pupils".
"His actions fell very short of the standards expected of a registered person and amounted to unacceptable professional conduct," he added.
Walsall have signed goalkeeper Mark Gillespie on a two-year contract from Carlisle United on a free transfer.
[NEXT_CONCEPT]
Cornish Pirates boss Ian Davies says ill-discipline "came back to haunt" his side in their 36-15 British and Irish Cup semi-final defeat at London Welsh.
[NEXT_CONCEPT]
A Carmarthenshire teacher who sent thousands of sexual messages to three pupils has been banned from teaching for five years.