Mitchell served as an officer in the 92nd Infantry Division during World War II, and was wounded in Italy; he received the Purple Heart.

Before entering graduate school, Mitchell participated in the early civil rights activity in Baltimore.

[3] In 1983 he joined with 7 other Congressional Representatives to sponsor a resolution to impeach Ronald Reagan over his sudden and unexpected invasion of Grenada.

As Chairman of the Small Business Committee, Mitchell attached an amendment to a $4 billion public works bill that compelled state and local governments, seeking federal grants, to set aside 10% of the funds to retain minority firms as contractors and subcontractors.

Mitchell initiated a congressional investigation into Wedtech where bribes were alleged to have been offered in return for no bid military contracts.

[5] Mitchell died on May 28, 2007, of pneumonia at Greater Baltimore Medical Center in Towson, Maryland, after being hospitalized for a week.

Congressman Elijah Cummings delivered the eulogy saying: "He earned the trust of people throughout the country and the world because he was constantly building bridges for others to cross, while tearing down the walls that had excluded them.

"[6] On December 3, 2015, the University of Maryland, College Park held a dedication ceremony renaming the Art/Sociology Building in his honor.