[2] After graduating law school, Garnett started her career as an associate at Wachtell, Lipton, Rosen & Katz in New York City from 2000 to 2004.

From 2005 to 2017, Garnett was an Assistant United States Attorney in the U.S. Attorney's Office for the Southern District of New York, which included service as Chief of Appeals from 2016 to 2017 and Chief of the Violent Crimes/Violent and Organized Crime Unit from 2011 to 2014.

President Biden nominated Garnett to the seat vacated by Judge Vincent L. Briccetti, who assumed senior status on April 21, 2023.

[7] On November 28, 2023, the United States Senate invoked cloture on her nomination by a 49–46 vote.

[10] Garnett lives in Brooklyn with her two children and her husband, Seth, a script supervisor for TV and film.