Sullivan began her career in immigration legal services more than 12 years ago. She earned her Juris Doctor cum laude from Fordham University School of Law, and her bachelor's degree in international relations from American University. She has been working in private practice, first as a paralegal and then as an attorney, covering the areas of family-based and employment-based immigration, as well as removal defense. Today, she represents CLINIC and its network in national coalitions, working groups and agency stakeholder engagements.

Sullivan has been an active volunteer, providing her services to Catholic Charities, the Norwegian Refugee Council, HIAS, the Dulles Justice Coalition, the American Immigration Lawyers Association, and the American Bar Association. She is admitted to the bar in Massachusetts and Rhode Island.