After graduating from law school, Richardson served as a law clerk for Judge Richard Posner of the United States Court of Appeals for the Seventh Circuit from 2003 to 2004 and for Chief Justice William Rehnquist of the Supreme Court of the United States from 2004 to 2005.

[1] Richardson then worked for three years at Kellogg, Hansen, Todd, Figel & Frederick in Washington, D.C., where he handled complex civil litigation.

Richardson notably prosecuted the mass murderer Dylann Roof for his actions during the Charleston church shooting.

[11] While Richardson served on the Fourth Circuit, the Court affirmed Dylann Roof's conviction and death sentence.

As Richardson served as the lead prosecutor, all of the judges on the Fourth Circuit recused themselves from reviewing Roof’s case.