Castner received her Bachelor of Science, cum laude, from The College of New Jersey in 2002 and her Juris Doctor, with honors, from Rutgers Law School in 2006.

[3] Castner served as a law clerk for Judge Joseph F. Lisa on the New Jersey Superior Court, Appellate Division, from 2006 to 2007.

She was then a partner at Montgomery McCracken Walker & Rhoads LLP in Cherry Hill, New Jersey, where her focus was on white collar criminal defense and product liability law.

[7] On January 3, 2022, her nomination was returned to the President under Rule XXXI, Paragraph 6 of the United States Senate;[8] she was later renominated the same day.

In 2018, Democratic Governor Phil Murphy named Bill Castner as his senior adviser on firearms.