She will make her debut in September's season premiere, the network said.
"Chenoweth will match wits with both Alicia and Peter in her role as a top-of-her-game political reporter who wants to know more about the Florrick campaign and marriage," the network said in a synopsis.
Julianna Margulies has earned Emmy, Screen Actors Guild and Golden Globe awards for her portrayal of attorney Alicia Florrick on the series. Chris Noth plays Peter, her formerly jailed politician husband, who was cleared in a corruption scandal and is now running for governor of Illinois.
Chenoweth won an Emmy for her work in "Pushing Daisies." She has also appeared on "Glee," "GCB" and "The West Wing." Her Broadway credits include "Wicked" and "Promises Promises."