The Ireland Under-21 international had an eight-game loan spell with the Saddlers in November and December.
"I had no qualms in bringing Aaron back, he had a really good spell with us before Christmas," boss Dean Smith told the club's website.
"Aaron will compete with David Grof and is a welcome addition to our squad."
McCarey added that he was delighted to have the opportunity to play more games.
"It's good to come back into a winning team that is moving in the right direction and hopefully I can play my part in this continuing," he said.
"I already know everyone at the club, so it will be an easy transition and I am looking forward to getting back into the swing of things."