Mark began his broadcast career in 1988 with Radio One, Inc. under the guidance of Cathy Hughes. His show, "Make It Plain", was the first talk show to sign on XM Satellite Radio in 2001. He was the first African American talk host on SiriusXM Progress, and one of few African Americans in the U.S. hosting a daily, national show on a progressive/liberal talk format.

He helped to organize the National African American Leadership Summit which grew out of the NAACP, under the leadership of the Rev. Dr. Benjamin F. Chavis, and he co-chaired the 1996 National Black Political Convention. He has emceed the Million Man March, every anniversary of the March on Washington, and the annual commemoration of Bloody Sunday in Selma, Alabama. He recently emceed the 20th Anniversary of the Million Man March.

Mark chaired the NAACP Metropolitan Police and Criminal Justice Review Task Force for the DC Branch. In that capacity, he co-authored legislation establishing the Board and Office of Police Complaints, and facilitated the beginning of an unprecedented study on racial profiling. He also taught courses in diversity awareness and cultural sensitivity at the DC Police Academy.

He is a Life Member of the NAACP, the National Action Network, the National Congress of Black Women and the National Organization of Women. Mark is also a frequent guest on numerous television networks.

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