Dennis Jacobs was born and educated in New York City and spent his entire career there as a lawyer and judge. He is a product of New York City public schools from kindergarten through college, and is a 1964 graduate of Queens College of the City University of New York.

He attended New York University Graduate School of Arts and Sciences from 1964 through 1970, was awarded a Masters degree in English literature at age 21 in 1965, and completed all requirements but dissertation for a Ph.D. in English before he left the Graduate School and crossed Washington Square to enroll at the School of Law. He has taught English at Queens College and at the Nassau County Police Science Academy.

He enrolled in New York University School of Law in 1970 and obtained his JD degree in 1973. He served on the Law Review and was a Pomeroy Scholar.

His entire career as a lawyer was at the Manhattan law firm of Simpson Thacher & Bartlett, where he became a partner in 1980. He appeared in courts in New York and around the country as a litigating lawyer in commercial matters on behalf of the clients of that firm.

In 1992 he was nominated by President Bush to a seat on the United States Court of Appeals for the Second Circuit that had previously been occupied by Wilfred Feinberg and before him by Thurgood Marshall.

As a judge, he has been awarded the Learned Hand Medal for excellence in jurisprudence by the Federal Bar Council, 2003; the Eugene J. Keogh Award for distinguished public service by New York University, 2004; the Outstanding Public Service Award by the New York Intellectual Property Law Association, 2009; and the James Madison Award by the Federalist Society. An honorary degree of Doctor of Laws was conferred in 2009 by St. John's University. He participates on panels, and speaks on legal subjects, and has participated in the Mentor Program for students in the New York City high schools.