Pierzynski, 37, replaces left handed reliever Sam Freeman on the Cardinals roster.
The addition of Pierzynski will allow allow the Cardinals to have another experienced bat on the bench and give the team flexibility to use backup Tony Cruz.
“It’s more so what A.J. brings more than anything else,” manager Mike Matheny said.
Marco Gonzales earned two wins and worked three scoreless innings in the National League Championship Series against the Los Angeles Dodgers making Freeman expendable.
Pierzynski was signed by the Cardinals following a release by the Boston Red Sox. He initially saw playing time with Yadier Molina on the disabled list.
“Obviously, you’re disappointed,” Pierzynski said of being left off the NLDS roster. “Once I got over the initial kind of frustration of it and I had a nice conversation with Mike and we talked about the reasoning, I was OK with it.
“I said, `Look, I’m going to do everything I can to help this team and be excited for the guys and try to be as positive as I can off the bench.”