She left her advertising career to attend the University of California, San Diego (UCSD), where she earned her M.F.A.
Marnich began writing for television when she joined the HBO drama Big Love as staff writer for the show's third season.
Since, she worked on Showtime's The Big C and The Affair (as co-executive producer); and for AMC's Low Winter Sun.
She has developed work with HBO, AMC, Silver Pictures, Amblin, Scott Free and TNT, and Amazon.
(Story by Dan LeFranc) The Francesca Primus Prize (Denver Center Theatre); the Mickey Kaplan New American Play Prize (Cincinnati Playhouse in the Park); the Carbonell Award for Best New Work of the Year; two McKnight Advancement Grants and two Jerome Fellowships (The Playwrights’ Center); the Melvoin Award (Northlight Theatre); and the Samuel Goldwyn Writing Award.