Lanthier received a Bachelor of Arts from Amherst College in 1993 and a Juris Doctor from Northeastern University School of Law in 1996.

From 2007 to 2024, she was the supervising attorney in the Rutland County Public Defender's Office.

[2] She is a past chair of the Vermont chapter of the American College of Trial Lawyers.

President Biden nominated Lanthier to the seat being vacated by Judge Geoffrey W. Crawford, who subsequently assumed senior status on August 9, 2024.

[6] On September 11, 2024, the United States Senate invoked cloture on her nomination by a 55–42 vote.