Brien focuses his practice on product liability matters, with primary emphasis on Engle-Progeny tobacco litigation. He is involved in all phases of pretrial and trial work, including motion practice and witness interviews. He also serves as a pro bono attorney ad litem in juvenile dependency matters. 

During law school, Brien interned for The Hon. Caryl E. Delano, U.S. Bankruptcy Court for the Middle District of Florida, and clerked for the Spielberger Law Group, an employment discrimination law practice. He also was actively involved in the Willem C. Vis International Commercial Arbitration Competition, winning first place in the Florida pre-competition round. Brien also served as President and Vice President of The Pillars, a law student organization dedicated to cultural understanding, societal awareness and community service.

Before becoming an attorney, Brien worked for Bank of America, developing and maintaining relationships with clients and business partners, and ensuring compliance with governmental regulations and best practices in lending, privacy and ethics.