[1] Lilly was a contract player for film producer Cecil B. DeMille in her youth, before dating actor Ronald Reagan in the 1950s after his divorce from Jane Wyman.
[1][3] Lilly was a socialite and wrote several books about people of great wealth including Glamor Girl (1977; with co-author Robin Moore) and Those Fabulous Greeks: Onassis, Niarchos and Livanos (1970).
[1][2] Lilly has been cited as, and claimed herself, that she was an inspiration for Holly Golightly, the lead character in Truman Capote's novella Breakfast at Tiffany's.
Lilly published an updated version of the book in 1984 as How to Meet a Billionaire, commenting that "A million dollars isn't much money these days.
"[1] Lilly wrote for several publications, including as a contributor to Avenue, Cosmopolitan, Ladies' Home Journal, McCall's magazines, as beauty editor of Town and Country.