Abraham was born in Elizabethtown, New Jersey. He was a surveyor and lawyer, and was clerk of the Provincial Assembly. Later he became High Sheriff of Essex County and in 1775 was elected to the Provincial Congress. He was a member of the Committee of Public Safety.
Early in 1776, the New Jersey delegation to the Continental Congress was opposed to independence from Great Britain. When the issue became most important, the state convention replaced all their delegates with men favoring the separation. On June 21, they appointed Clark, along with John Hart, Francis Hopkinson, Richard Stockton, and John Witherspoon as new delegates. They arrived in Philadelphia on June 28 and signed the Declaration of Independence in early July.