Costello earned a Bachelor of Arts, summa cum laude, from Temple University in 1998 and a Juris Doctor, magna cum laude, from Temple University Beasley School of Law in 2001.

She served for eight years as a cyber-systems operator, receiving an honorable discharge in 1994 as a staff sergeant.

From 2008 to 2024, she served as an assistant United States attorney in the U.S. Attorney's Office for the Eastern District of Pennsylvania,[2] where she prosecuted cases that include public corruption, fraud, and drug trafficking.

President Biden nominated Costello to the seat vacated by Judge Cynthia M. Rufe, who assumed senior status on December 31, 2021.

[7] On September 17, 2024, the United States Senate invoked cloture on her nomination by a 54–42 vote.