Attorney O'Brien worked as a prosecutor for nearly 10 years in Northern and Southern Virginia. In that role, Attorney O'Brien prosecuted primarily serious felony offenses, including homicide, drug distribution and possession charges, and white-collar offenses. Additionally, Attorney O'Brien worked with the Commonwealth Attorney's Services Council training all prosecutors throughout Virginia in electronic evidence and cutting edge trial presentation techniques. Furthermore, Attorney O'Brien trained numerous police officers in proper procedures relating to DWI and DUI.