He graduated from Bladensburg High School in 1968, and Johns Hopkins University in 1972 with a degree in political science.

[2] After serving as a legislative aide for the Prince George's County Council from 1970 to 1974, and the Chief of Staff for the Prince George's County Executive from 1974 to 1978, McDonough practiced law as an associate and partner in various firms from 1979 to 2005, including the firm of O'Malley, Miles, Nylen & Gilmore where he was a managing partner for ten years.

As Secretary of State, McDonough oversaw the registration of notaries and charitable organizations and served as the governor's liaison for labor relations.

McDonough married Mary Lou Gober in 1972 and the couple has three daughters, Emily, Caitlin and Aisling.

[4] Daughter Caitlin McDonough served as Legislative Director to Senate President Thomas V. "Mike" Miller Jr. from 2006 to 2012 and is married to Delegate Ben Barnes, who chairs the House Appropriations Committee.