She holds a master's in environmental policy from Duke University's Nicholas School of the Environment and worked for Natural Resources Defense Council for two years before joining the Center for Biological Diversity in 1999 as a staff writer.

Her first book, Omnivores (1996), is a subversion of the coming-of-age novel, in which a young girl in Southern California is tormented by her megalomaniac father and invalid mother and finally sold in marriage to a real estate agent.

She has coolly avoided injecting so much as a hint of it into this thin, sharp and frequently funny novel; one of the narrator's salient characteristics is an inability to feel even the mildest indignation.

Sarah Weinman of the Washington Post Book World called it "both prism and truth" "With a sharp eye for small details, a keen sense of the absurd and strong empathy for its creations," Millet creates a kaleidoscope of quirky characters.

It features a young Los Angeles real estate developer consumed by power and political ambitions who, after his mother's suicide attempt and two other deaths, begins to nurture a curious obsession with vanishing species.

Eye Weekly summarized this black comedy, noting "American culture loves its stories of hubris, downfall and ruin as of late, but it takes a writer of Millet's sensitivity to enjoy the way down this much."

In a moment of drunken heroism, Hal embarks on a quest to find the man, embroiling himself in a surreal tropical adventure (and an unexpected affair with a beguiling German woman).

The Boston Globe called it "[An] odd and wonderful novel", while the Cleveland Plain Dealer wrote, "Millet is that rare writer of ideas who can turn a ruminative passage into something deeply personal.

Jonathan Lethem, writing for The Guardian, called it "elegant, darkly comic…with overtones variously of Muriel Spark, Edward Gorey and J. G. Ballard, full of contemporary wit and devilish fateful turns for her characters, and then also to knit together into a tapestry of vast implication and ethical urgency, something as large as any writer could attempt: a kind of allegorical elegy for life on a dying planet.

Beginning with The Fires Beneath the Sea, the plot follows two young siblings as they search for their mother, a shapeshifting character who is fighting against forces who wants to make the planet over in their own image.

Sweet Lamb of Heaven, published by W. W. Norton & Company in May 2016, blends domestic thriller with psychological horror, following a young mother's flight from her cold and unfaithful husband.

He spends his time volunteering at a local women's shelter and wrestling with his breakup and the possibility of future romance in middle age, while also learning about birds that populate the area – which are the descendants of "dinosaurs" referenced by the title.