James O’Sullivan is a left-of-center activist and career nonprofit manager. While he works as a senior staffer of Stand Up To Cancer, an organization ostensibly dedicated to fighting cancer, he previously spent decades at organizations promoting left-of-center policies and social movements.
O’Sullivan has also sat on the boards and committees of several prominent left-of-center philanthropic entities and their subordinate projects. 
After spending several years at the Charles A. Dana Foundation, which primarily supports neuroscience and mental disorder research, James O’Sullivan became a program officer in 1996 at the Open Society Foundations, the grantmaking organization of left-wing billionaire financier George Soros. O’Sullivan worked for OSF’s Center on Crime, Communities, and Culture, for which he created a grant program for former convicts and managed the foundation’s coordination with other left-progressive criminal justice grantmaking organizations in the United States. 
After two years at the Open Society Foundations, O’Sullivan accepted a senior program officer position at the John A. Hartford Foundation, where he oversaw grant programs related to medicine, social services, and healthcare policy. A decade later, he joined Rockefeller Philanthropy Advisors, a leading left-of-center grantmaking organization, as the director of its foundation services team. Rockefeller’s grant recipients include the New Venture Fund, an influential philanthropy which also serves as an incubator for a wide range of new and growing left-of-center groups, and the Planned Parenthood Federation of America, a major abortion provider and promoter. O’Sullivan primarily oversaw grantmaking initiatives related to public health and medical research, but also managed funding for left-of-center cultural initiatives, both in the United States and elsewhere. 
In 2013, James O’Sullivan joined the Leona M. and Harry M. Helmsley Charitable Trust, taking on a dual role as program director of one of the organization’s medical research initiatives and as senior advisor for its program in Israel. The Helmsley Charitable Trust chiefly focuses on medicine and healthcare but has also funded left-of-center environmental initiatives and played a role in developing the controversial Common Core education curriculum implemented under the Obama Administration. In 2016, O’Sullivan became director of philanthropy and corporate relations for the advocacy group Stand Up To Cancer and also began offering nonprofit consulting services to left-of-center organizations, including a New York City-based gay and lesbian activist group. O’Sullivan would go on to join the group’s board of directors. 
James O’Sullivan completed his bachelor’s degree at the State University of New York at Albany, majoring in history and journalism. In 1996, he received a master’s degree in public health from Columbia University, and in 2005, he completed a second master’s degree in nonprofit and public organizational management from New York University. 
James O’Sullivan is the co-chair of the International Grantmakers Network, a project of the charitable organization Philanthropy New York. He also sits on the national advisory board of a healthcare policy program funded by the now-defunct left-progressive grantmaking collective Atlantic Philanthropies, and the national advisory committee of an awards program of the Robert Wood Johnson Foundation. In addition, he has been an adviser to several smaller New York-based charitable projects, including a charter school in New York City and a natural disaster recovery assistance committee also associated with Philanthropy New York.