Chernus will play "a dynamic, groovy pastor of a Church that Adam (Gabriel Basso) starts to attend", reports TV Line.
The Showtime drama series follows the life of suburban mum Cathy Jamison (Laura Linney), who is diagnosed with cancer.
The Big C, which was previously renewed for a third season, recently promoted Gabourey Sidibe to a series regular.
The new season will return to Showtime on April 8.
Chernus previously starred in Love and Other Drugs, and can be seen in the upcoming Men in Black III and The Bourne Legacy.
Watch a clip of The Big C below: