[3] Greenfield's undergraduate thesis helped kick start her career as an intern for National Geographic Magazine.

A subsequent grant from National Geographic provided financial support toward her debut monograph, "Fast Forward: Growing Up in the Shadow of Hollywood" (Knopf 1997).

[4] Five years after the release of "Fast Forward", Greenfield produced a second major body of work about the self-esteem crisis amongst American women, entitled "Girl Culture".

This experience exposed her to anthropological and documentary filmmaking in France, Yugoslavia, Hungary, Austria, India, Australia, and Japan.

In a 2012 interview with Sara Melson (for Harvardwood.com), Greenfield was quoted as saying "We watched many indigenous films, and we met with amazing directors.

[7][8] In 1988, she co-directed a 25-minute film, Once You're In, with Harvard classmate Rachel Watanabe-Batton about Irish illegal immigrants living in Boston.

[9][10] Greenfield subsequently directed THIN, a feature-length documentary for HBO,[11] and published an accompanying book with the same title.

In September 2006, Greenfield received the prestigious Grierson Award for best documentary shown at the BFI London Film Festival.

[14] In 2020, fiction author Elle Nash wrote a short story about THIN on HARSH Lit Mag.

[33] In January 2013, Greenfield was nominated by the Directors Guild of America (DGA) for Outstanding Directorial Achievement in Documentaries for the year 2012.

[50] In January 2015, Greenfield was nominated by the Directors Guild of America (DGA) for Outstanding Directorial Achievement in Commercials for the year 2014.

[76][77] Nick Allen of RogerEbert.com wrote that the film was "a stunningly deeply resonant documentary about notions as seemingly obvious as the value of love over wealth itself.

"[78] Ann-Derrick Gaillot's generally positive review in The Outline described it as a "a sprawling chronicle of decadence and decay" and "As a study of capitalist obsession, it’s a fascinating and at times frantic look at the very bizarre world we are all strangely accustomed to.

"[79] Joseph Walsh of Time Out praised it for laying bare society's obsession with affluence and excess with "scalpel-sharp insight."

He found the documentary to be bleak yet compelling, suggesting that it effectively captures and critiques societal trends around wealth and consumerism.

The show was exhibited in France, the Netherlands, Italy, Russia and a number of cultural venues in North America.

[109] The success of her second monograph, Girl Culture (2002),[5] and the accompanying show helped to cement her worldwide reputation as a documentary photographer.

[117] In 2016 the International Center of Photography honored Greenfield with a Spotlight Award for her "extensive contributions to the visual storytelling world.

[122] According to the Annenberg Space for Photography website, this exhibition covers "the influence of affluence over the last 25 years, illustrating the globalization of materialism, celebrity culture and social status," and contains "195 color-saturated prints, 42 riveting first-person interviews and the accompanying multimedia projections and short films".

[123][124] Writing about the Generation Wealth exhibit for Artforum, Naomi Fry noted, "[W]hat makes Greenfield’s photographs multilayered, sensitive, and fascinating—and carries them beyond a single-minded morality tale—is her understanding that people’s relationships with things in this lurid world are pleasurable and miserable both.