Both actresses will appear in Californication's seventh season premiere, with Graham portraying a mystery woman from Hank's (David Duchovny) past.
Former 24 star Rajskub has been enlisted to play a neurotic writer, according to Entertainment Weekly.
Californication's seventh season will also feature Emmy-winning Sopranos actor Michael Imperioli joining the cast as a television producer who helps Hank pull off his latest scheme.
Duchovny stars in the Showtime series as a troubled writer who struggles to control his sex addiction, while dealing with a dysfunctional family.
Showtime is expected to premiere Californication's next season in 2014.