Keisler was born in Hempstead, New York. A 1977 graduate from George W. Hewlett High School in Long Island, he went to Yale University both for undergraduate and law school. As an undergraduate, Keisler was the Chairman of the Party of the Right (Yale) and the Speaker of the Yale Political Union. He graduated "magna cum laude" from Yale College in 1981 and then entered Yale Law School. In 1982, he helped to co-found the Federalist Society, a conservative thinktank. He received his J.D. in 1985. After law school, Keisler clerked for Judge Robert Bork on the D.C. Circuit from 1985 to 1986. After this clerkship, he joined the Office of Legal Counsel under President Ronald Reagan. There, he worked on both the Supreme Court nominations of his former boss, Robert Bork, and the man who replaced Bork as a Supreme Court nominee, Justice Anthony Kennedy. After Kennedy was confirmed, he hired Keisler to be one of his four law clerks during his first year on the Court in 1988. One of his fellow clerks during that year was Miguel Estrada, another conservative nominee to the D.C. Circuit whose nomination was controversially filibustered by the Democrats in 2003.