First Assistant Erin O'Brien

First Assistant Erin O’Brien began her career as a prosecutor in the Philadelphia District Attorney’s Office in 2005, serving in the Municipal Court, Juvenile and Felony Waivers Units then joined the Family Violence Unit as a trial attorney in September 2007. Ms. O’Brien joined the Chester County District Attorney’s Office in April 2017 as a trial attorney and has continued to service the community by prosecuting high-level child abuse cases and working to educate the Chester County area on child advocacy.

Throughout her time at the Philadelphia District Attorney’s Office, Ms. O’Brien supervised the domestic violence, sexual assault, and child physical and sexual abuse investigations and prosecutions for the City of Philadelphia. In her capacity as a trial attorney in both Philadelphia and Chester counties, Ms. O’Brien has tried more than 90 domestic violence, sexual assault, and child abuse jury trials and handled thousands of child abuse, neglect, and sexual assault investigations involving the most vulnerable victims.  

From 2013-2017, Ms. O’Brien served as the prosecutor on site at the Philadelphia Safety Collaborative, a co-located multi-disciplinary facility for child abuse and sexual assault investigations, and as the DA’s Office representative to the Philadelphia Anti-Human Trafficking Task Force and the Philadelphia Autism Task Force.  

Ms. O’Brien also serves as a Special Assistant United States Attorney handling child sexual exploitation cases and serves on the board of SCAN/Prevent Child Abuse PA, the Pennsylvania Medical-Legal Advisory Board, and the newly-formed Medical Forum Leadership Team for the state.  

As a Chester County resident, Ms. O’Brien continues to dedicate herself to fighting for the justice of victims and also to raising her two sons alongside her husband.

Ms. O’Brien received her J.D. from the Beasley School of Law at Temple University in 2005, and her B.A. in Criminal Justice from American University in 2002.

Erin O Brien Headshot