Mark Potok (born January 1, 1955) is an American writer, journalist, and leading expert on extremism and hate groups. Raised in Plainfield, Vermont, he graduated from the University of Chicago between 1974 and 1978 with a bachelor's degree. He began his career as an award-winning journalist, spending nearly two decades reporting for major newspapers including USA Today, the Dallas Times Herald, and The Miami Herald. In 1997, he joined the Southern Poverty Law Center (SPLC), a prominent civil rights nonprofit based in Montgomery, Alabama, where he served as editor-in-chief of the organization's quarterly Intelligence Report journal and as the director of the Intelligence Project, overseeing the monitoring, designation, and reporting on hate groups, including anti-Muslim activists and organizations. He was a senior fellow at the SPLC from 2000 to 2017, specializing in tracking hate groups, extremist ideologies, and extremist funding networks. He led investigations into hate groups and authored reports designating organizations like FAIR as nativist groups promoting anti-immigrant rhetoric. During his tenure, Potok became a prominent spokesman on issues of hate groups, right-wing extremism, and domestic terrorism, specializing in tracking extremist groups such as white supremacist organizations and other radical right entities. He testified before bodies including the U.S. Senate, the United Nations High Commission on Human Rights, and the Helsinki Commission, authored and edited numerous investigative reports, contributed to the Hatewatch blog, and appeared frequently in media outlets. He received awards including a 2010 first-place Green Eyeshade Award for investigative journalism. After leaving the SPLC in 2017, Potok continued his research as a senior fellow at the Centre for Analysis of the Radical Right (CARR), where he studies right-wing populism and is writing a book on the subject. He has delivered keynote speeches at venues such as the U.S. Holocaust Memorial Museum and participated in events addressing Islamophobia and extremism.

Potok's career has attracted controversy. Critics, including researcher Laird Wilcox, have accused him and the SPLC of inflating the threat from far-right groups for fundraising purposes, with Wilcox claiming that over half of the SPLC's listed 'hate groups' were inactive or nonexistent as of 2010. Potok has stated that the SPLC's goal is to 'destroy these groups' ideologically, acknowledging that listings are based on ideology rather than criminality. Additional critics, including some conservative outlets, have labeled Potok and the SPLC as partisan, accusing them of broadly painting conservative movements like the Tea Party as riddled with racism and conspiracy theories. Despite such criticisms, Potok remains a key figure in monitoring extremism and promoting awareness of hate networks in the United States.