Her mother was a member of the Denishawn Dance Company and her father, Earl Moran, an artist specialising in pin-up portraits.
In late August, 2002, Peggy Moran was a passenger in a car involved in a serious automobile accident in Oxnard, California. She broke her neck, leg and several ribs as well as puncturing one of her lungs.
Though retired for nearly 60 years, Peggy developed minor cult fame over the years thanks to her "scream queen" roles in The Mummy's Hand (1940) and Horror Island (1941) at Universal in the early 40s. She frequently flew to conventions all over the country and was invited in 2001 to Universal's premiere of The Mummy Returns (2001) with Brendan Fraser.
When she married Henry Koster in 1942, he promised to put her in every movie he made in the future and he did. He had a bust of her head made and it was used in all of his films after their marriage.