In the 1976 United States House of Representatives Elections, Marks defeated the Pennsylvania six-term Democratic incumbent Joseph Vigorito with an 11% margin, one of eight Democrats unseated nationwide. He defeated Vigorito again in the 1978 election with a 26% margin, and state RepresentativeDavid C. DiCarlo in 1980 by 120 votes. A serious back ailment led him to not seek re-election for a fourth term in 1982.[2] This decision prompted a speech to the House of Representatives in March 1982, before House Speaker Tip O'Neill, in which he brought into question his own support of Reaganite policies, that, he argued, had an undue emphasis on military spending, and had caused distress to those to whom he defined as "disadvantaged".[3] Prior to leaving Congress, John B. Connally talked to Marks and considered him as a running mate, during Connally's failed 1980 Presidential bid.[4]
