Sarek, who was first introduced in the original Star Trek, has made appearances throughout the franchise's 50-year history.
READ: Star Trek Legends Wish The Series A Happy 50th Anniversary
Frain joins previously announced stars Doug Jones, Michelle Yeoh, Anthony Rapp, Chris Obi, Shazad Latif, and Mary Chieffo.
The new series will take place about 10 years before Captain Kirk's five-year mission.
Stream all-new episodes of Star Trek: Discovery Sundays at 8:30 PM ET / 5:30 PM PT, exclusively on CBS All Access.