Vincent DeMarco was born on May 23, 1957 in Trevico, Italy. His family moved to the US when he was four and settled in New Jersey. Through a joint Advanced Interdisciplinary Legal Education Program between Johns Hopkins University and Columbia University School of Law, in 1979 DeMarco earned his B.A. in Political Science at Johns Hopkins in three years, and then went to Columbia to earn his J.D. in 1980. During his summers there he interned in the U.S. House of Representatives. In 1976, he was an intern with the Small Business Committee and in 1977 he was an intern with the Education and Labor Committee. During the summer between Johns Hopkins and Columbia, he worked as a law clerk at the law firm of Covington and Burling. After receiving his J.D., he was a law clerk for Chief Justice Robert N. Wilentz of the Supreme Court of New Jersey from November 1980 to August 1981.

In 1982, he earned his Master of Arts in American History at Johns Hopkins University. From July 1982 to June 1983, he worked as a staff attorney in the Maryland Attorney General's Office. Then from October 1983 to December 1992 he was Assistant Attorney General for the Maryland Attorney General. He resigned that position in order to help the then Attorney General, Stephen H. Sachs, run for Governor of Maryland. He also held the title of President of the Young Democrats of Maryland between 1983 and 1985. In 1988 DeMarco worked hard as Campaign Manager for Citizens for Eliminating Saturday Night Specials to pass this unprecedented legislation in Maryland. In 1990 he was also a Campaign Advisor for the Curran for Attorney General Campaign. From January 1993 to December 1994 he was an associate at the law firm of Prem and Dumler. He was also the Executive Director for Marylanders Against Handgun Abuse (MAHA).