Leigh Bienen graduated from Cornell University in 1960 and undertook graduate work in Economics at M.I.T., and Creative Writing at the University of Iowa before completing her J.D. from Rutgers in 1975. After her admission to the Bar of the Supreme Court of New Jersey in 1975, Bienen wrote on rape law reform in the late 1970s and early 1980s while working briefly as a Research Attorney at the Center of Rape Concern at Philadelphia General Hospital. During this time she also lectured in the Politics Department at Princeton, the University Of Pennsylvania School Of Law, and briefly at the University of California-Berkley School of Law.

Bienen first joined the New Jersey Department of the Public Advocate in 1977 as Assistant Deputy Public Defender and became Director of a Special Projects Section devoted to studying state's use of capital punishment. Here she directed the New Jersey Public Defender Homicide Study, an empirical study that examined the state's restoration of the Death Penalty in 1982. The culminating report of the project, The Reimposition of Capital Punishment in New Jersey was cited in State v. Ramseur, the first capital punishment challenge to the New Jersey Supreme Court since 1982. Findings from the study were published in the Rutgers Law Review and the Albany Law Review with Bienen as lead author. Co-authors included Neil Alan Weiner and Deborah W. Denno, other notable death penalty scholars, and Douglas A. Mills, a statistical programming consultant.

The Public Defender Homicide Study influenced the state supreme court which ordered an empirical proportionality review of New Jersey capital cases. Proportionality review is the analysis of an individual death sentence when compared to similar sentences imposed upon similar defendants for similar crimes. Professor David C. Baldus was appointed Special Master to the New Jersey Supreme Court where he developed the methodology for collecting and analyzing data for the project. The state Public Defender contributed data from the Homicide Study and Baldus developed a public collection of data on all relevant homicide cases and headed the New Jersey Proportionality Review Project which included Leigh Bienen. The Project met regularly for three years while they debated the identification of death-eligible cases and all relevant legal and factual issues.

The New Jersey Proportionality Review Project was cited and debated in State v. Marshall II, the first case where the state supreme court conducted proportionality review. The results of the Project suggested race-of-defendant bias, but was criticized due to the overall instability of the data models. Furthermore, the State Attorney General's Office contended that the "universe" of cases included by the Project was too broad and argued that only similar death sentences--not all death-eligible cases--should be included. Robert O. Marshall became the first of 36 New Jersey capital defendants to have his death sentence upheld by the New Jersey Supreme Court on appeal since 1982. In 1992 the New Jersey State Legislature passed a law that enforced the State Attorney General's Office's option that comparison cases in proportionality review would be limited only to cases where a death sentence was imposed. Robert O. Marshall's death sentence was overturned in 2006 and New Jersey abolished capital punishment in 2007, becoming the first state to do so by legislative act.

Leigh Bienen joined the Woodrow Wilson School of Public and International Affairs as a Lecturer and Administrative Director of the Undergraduate Program in 1991, although she continued to work as a consultant to the New Jersey Department of the Public Advocate for some time. While at Princeton her researched examined proportionality review in state supreme courts and the role of prosecutor discretion in the imposition of the death penalty.

In 1995, Bienen joined the Northwestern University School of Law as a Senior Lecturer. She began researching and writing on the monetary costs of capital punishment, developed the Northwestern University Law School Capital Crimes Database and the Chicago Historical Homicide Project. In 2006 she was appointed a member of the Illinois Capital Punishment Reform Study Committee, a group that was established by Governor George Ryan after his moratorium on executions in 2000 to examine if the death penalty could be carried out fairly. After the committee's final report in 2011, the state legislature repealed the death penalty that year.