The Scream star will play one of his character Dr. Derek Shepherd's four sisters in two episodes that will air in the U.S. in December (12), according to TVGuide.com.
Embeth Davitz and Caterina Scorsone have appeared as Shepherd's siblings in previous episodes.
Campbell's latest TV role will be a reunion of sorts - she and Dempsey co-starred in Scream 3.
The Private Practice star was assisted by midwives for the delivery at her home in Los Angeles, and daughter Eliza arrived on Friday (06Jul12).
The little girl is Scorsone's first baby with her rocker husband Rob Giles, and they are delighted with the new addition to their family.
The couple tells People.com, "We couldn't be more in love with her and are overflowing with gratitude for this beautiful miracle."
The Private Practice star is expecting rocker husband Rob Giles' child later this year (12).
Her pregnancy has been written into the hit U.S. medical drama, courtesy of creator Shonda Rimes - her character Dr. Amelia Shepard will reveal she is pregnant on Thursday night's (23Feb12) episode.
She tells People.com, "The (baby) news came out of left field and I think she (Rimes) decided she could use this for dramatic purposes."