Sarah Greenough is senior curator and head of the department of photographs at the National Gallery of Art. In 1978, she was awarded a Samuel H. Kress Fellowship at the National Gallery, where she has worked ever since. In 1990, she became the founding curator of the department of photographs and has been responsible for establishing and growing the National Gallery's collection of photographs. She also established the program for photography at the National Gallery, which now presents two to three photography exhibitions per year in the museum's dedicated photography galleries, as well as many smaller installations.

During her time at the National Gallery she has organized numerous exhibitions, including Alfred Stieglitz (1983), On the Art of Fixing a Shadow: 150 Years of Photography (1989), Modern Art and America: Alfred Stieglitz and His New York Galleries (2001), André Kertész (2005), Irving Penn: Platinum Prints (2005), Looking In: Robert Frank's "The Americans" (2009), and Beat Memories: The Photographs of Allen Ginsberg (2010), all of which have also traveled to museums around the world. She was co-curator of The Art of the American Snapshot, 1888-1978: From the Collection of Robert E. Jackson (2007), Impressed by Light: British Photographs from Paper Negatives, 1840-1860, (2008), Tell It with Pride: The 54th Massachusetts Regiment and Augustus Saint Gaudens' Shaw Memorial (2013), Garry Winogrand (2013), The Memory of Time: Contemporary Photographs at the National Gallery of Art (2015), and Sally Mann: A Thousand Crossings (2018), and curator of Harry Callahan at 100 (2011), Photography Reinvented: The Collection of Robert E. Meyerhoff and Rheda Becker (2016).

Greenough is the author of many publications, including Walker Evans: Subways and Streets (1991), Robert Frank: Moving Out (1994), Harry Callahan (1996), Alfred Stieglitz: The Key Set (2002), All the Mighty World: The Photographs of Roger Fenton, 1852–1860 (2004), with Malcolm Daniel and Gordon Baldwin, The Altering Eye: Photographs from the National Gallery of Art (2015), with Sarah Kennel, Andrea Nelson, Diane Waggoner, and Philip Brookman, and author and editor of My Faraway One: Selected Letters of Georgia O'Keeffe and Alfred Stieglitz, Volume One, 1915-1933, Yale University Press (2011).

Her exhibitions and publications have won many awards, including the International Center of Photography Publications Award for On the Art of Fixing a Shadow: 150 Years of Photography and the George Wittenborn Memorial Book Award for Alfred Stieglitz: The Key Set for outstanding art publication of the year. In 2007, Greenough and co-author Diane Waggoner won the College Art Association's Alfred H. Barr, Jr. award for outstanding museum scholarship for their exhibition catalog, The Art of the American Snapshot: 1888–1978. In 2009, Greenough won the Outstanding Museum Catalogue of the Year from the Association of Art Museum Curators' award for Looking In: Robert Frank's "The Americans," and in 2010 she won the International Center for Photography's Infinity Award for Publications for the same publication.

Greenough received her PhD and MA from University of New Mexico where she studied with the noted photographic historian Beaumont Newhall. She also holds a BA from the University of Pennsylvania.