Hardy Cross Dillard was born in New Orleans in 1902, the second son of Dr. James H. Dillard and Avarene Budd Dillard. Dr. Dillard, a professor of mathematics, literature and classics, also served as dean at Tulane University. In 1911 the family moved to Paris where Hardy learned French and received his early schooling. Later the family settled in Charlottesville, and Hardy spent most of his preparatory school years at Virginia Episcopal School in Lynchburg. After one year at the University of Virginia, he transferred in 1920 to the U.S. Military Academy. Upon graduation in 1924, he returned to the University of Virginia to study law.

During his law school years, Hardy was an outstanding student and an editor of the Virginia Law Review. After graduation in 1927, he accepted the invitation to serve as acting professor at the Law School for a couple of years. He then spent a year practicing law in New York and a year as a Carnegie Endowment Fellow at the University of Paris before returning to teach law at Virginia where he would remain a member of the faculty until retirement in 1968. Dillard taught and wrote on the subjects of contracts, international law, and jurisprudence, among others. In time he became one of the best loved and most respected members of the Law School community in the twentieth century. In 1963 he began a five-year term as dean. A couple of years after his retirement he was appointed judge on the International Court of Justice at The Hague where he served until 1979.

In tandem with his career in legal education, Dillard had a military career. In 1942 he offered his service to the U.S. Army and quickly achieved the rank of colonel, serving in Europe and the Far East. For many years after the war, he held various advisory positions at the National War College and the U.S. Air Force Academy.

During the turbulent years following the Supreme Court's decision in Brown v. Board of Education, Dillard took a leadership role in opposing Virginia's advocates of massive resistance. In 1955 he argued for the defense before the Virginia Supreme Court in Almond v. Day, a case testing the legality of laws giving veterans' orphans grants to be used for either public or private schooling. Virginia's Comptroller Day had refused to pay these grants on the grounds that they were unconstitutional, and the Court agreed. Through the 1960s Dillard worked determinedly in support of the integration of Virginia's public schools.

Hardy Dillard married Janet Schauffler, and they had a daughter, Joan, and a son, Hardy. Janet died in 1970, and two years later Hardy married Valgerdur Dent. He died in Charlottesville in 1982.