"Kevin has played at a higher level and has the experience, ability and quality that we need," said Walsall manager Richard Money.
Cooper, 32, had a four-game spell at Yeovil Town earlier this season.
He featured in the Bluebirds side in December and January, but has since fallen down the pecking order at the Championship club.
Money added: "We are only too aware that we need something extra in the final third and both Kevin Cooper and Kevin Harper, who we signed on Thursday, will provide it.
"I have spoken with Kevin at length this morning and he likes the way we play; he is keen to be part of our promotion push and that extra quality he possesses is just what we are looking for.
"I want us to be as strong as we can be for the final run-in, so I wouldn't rule out any further deals in the weeks ahead."
BBC