He was a law clerk for Judge Henry Friendly of the United States Court of Appeals for the Second Circuit from 1963 until 1964.
From 1969 until 1975, Leval was in private law practice as an associate and then a partner in the New York firm of Cleary, Gottlieb, Steen & Hamilton.
The article argued that the most critical element of the fair use analysis is the transformativeness of a work, the first of the statutory factors listed in the Copyright Act of 1976, 17 U.S.C.
[3] Leval was nominated by President Bill Clinton on August 6, 1993, to a seat on the United States Court of Appeals for the Second Circuit vacated by Judge George C. Pratt.
He was awarded the Hillmon Memorial Fellowship by the University of Wisconsin–Madison in 1988; the Donald R. Brace Memorial Lectureship by the Copyright Society of the U.S.A. in 1989; the Fowler Harper Memorial Fellowship by Yale Law School in 1992; the Melville Nimmer Lectureship by UCLA Law School in 1997; the Learned Hand Medal of the Federal Bar Council in 1997; and the University of Connecticut School of Law's Intellectual Property Keynote Lectureship for 2001.