Cummings was born in Baltimore, the son of Ruth and Robert Cummings. He has a younger brother James. He graduated with honors from Baltimore City College in 1969. He later attended Howard University in Washington, D.C., where he served in the student government as sophomore class president, student government treasurer and later student government president. He became a member of the Phi Beta Kappa Society and graduated in 1973 with a Bachelor of Arts in Political Science.
Cummings graduated from law school at the University of Maryland School of Law, receiving his J.D. in 1976. He was admitted to the Maryland Bar in December 1976. He practiced law for 19 years before first being elected to the House in the 1996 elections.
Also after graduating from law school, Cummings received 12 honorary doctoral degrees from different universities across America.
For 14 years, Cummings served in the Maryland House of Delegates. In the Maryland General Assembly, he served as Chairman of the Legislative Black Caucus of Maryland and was the first African American in Maryland history to be named Speaker Pro Tempore, the second highest position in the House of Delegates.