Treanor graduated summa cum laude and Phi Beta Kappa from Yale College in 1979, where he was an active member of the Yale Political Union. He obtained an M.A. in history from Harvard University in 1982. He then entered Harvard Law School, but transferred to Yale Law School because he felt they focused more on public service. He was Article and Book Review Editor of the Yale Law Journal and graduated with a J.D. in 1985.
On October 15, 1994, Treanor married Allison Derivaux Ames, who was then director of strategic planning for corporate publicity and special events at Saks Fifth Avenue in New York City. He now has two children, Liam and Katherine.
Treanor's biggest commitment remains to legal scholarship. "William Treanor represents a new generation of scholars and teachers at Fordham's School of Law," said the Rev. Joseph A. O'Hare, S.J., president of Fordham University at the time of Treanor's appointment. When he first arrived to teach at Fordham in 1991, he evidenced his broad command of legal subjects in courses such as property, land use, intellectual property, constitutional law, criminal law, and legal history. In 1998, he went on leave from the university to serve as deputy assistant attorney general in the Justice Department's Office of Legal Counsel, before he returned to assume his current position in 2002.
"As dean of the law school, you're required to do both broad-level thinking and strategic planning," said Treanor in regard to challenges as a law dean. On July 17, 2006, Treanor announced to students and faculty that the school surpassed the $20 million mark for new gifts and pledges. This was in stark contrast to the levels reached in 2004 ($4.2 million) and 2005 ($6.9 million). The funds will help establish six new chairs and start the Feerick Center for Social Justice and Dispute Resolution, named in honor of Treanor's predecessor, John Feerick.
Plans for a new skyscraper were unveiled to accommodate increasing enrollment numbers, and the school ranks fifth in the country in placing its graduates at top-shelf law firms. But Treanor is not just concerned with growth and reputation. Like the law deans of Harvard (which built a state-of-the-art law student gym, limited class size to 80 students, and mandated individualized written feedback for every student in every course throughout the semester), and Yale (which abandoned the traditional law school grading system, does not rank its students, and has only one semester of required classes), Treanor has attempted to address the students' quality of life. In a 2006 interview, Treanor reported instituting free cupcakes and ice cream to alleviate the intensity of law school finals. Gifts to students, though, are in the offing: At the end of the 2006 academic year, Treanor worked for the purveyance of free flip-flops with Fordham's imprint on the bottom. "I feel obliged to make the Fordham experience for our students as special as possible," said Treanor. Fordham maintains a strict grading curve policy, class rankings, and a year-long 1L curriculum.
On June 29, 2010, it was announced that Dean Treanor would become the new executive vice president and Dean of Georgetown University Law Center, beginning August 16, 2010.
Since Treanor’s arrival, Georgetown Law has expanded the number of certified experiential offerings from 450 to more than 2000 seats and created four new clinics. Recognizing the need for lawyers to expand their skill set in a competitive market, he helped launch the Georgetown Law Business Skills Program and the Institute for Technology Law and Policy.
During Treanor’s tenure, Georgetown Law established a new program of post-graduate fellowships, which offer intensive training and opportunities for graduates to start public service careers. In 2015, in conjunction with the law firms DLA Piper and Arent Fox, Georgetown Law launched the D.C. Affordable Law Firm, an innovative “low-bono” model serving lower-income residents who cannot afford a lawyer but do not qualify for free legal aid. In 2016, the Law Center joined with Georgetown’s Medical Center and School of Medicine to create a medical-legal partnership—the Georgetown University Health Justice Alliance—dedicated to improved health and greater justice for those living in poverty
In 2012, Treanor was named a "champion" by the National Law Journal, one of the 25 "most influential in legal education" by the National Jurist and a recipient of the Dave Nee Foundation's David S. Stoner Uncommon Counselor Award.
Treanor's career in the public sector began as a speechwriter for Secretary of Education Shirley Hufstedler, followed by a clerkship for Judge James L. Oakes of the U.S. Court of Appeals for the Second Circuit. During the Iran-Contra Investigation, Treanor served as associate independent counsel. Later he became deputy assistant attorney general in the Office of Legal Counsel, responsible for supplying advice to the White House and attorney general.
Treanor has been cited in Supreme Court opinions twice, including by Chief Justice William Rehnquist in his dissent in Tahoe-Sierra Preservation Council, Inc. v. Tahoe Regional Planning Agency. He has written in-depth about some of the most controversial and complex turn of the 20th century constitutional law issues. He examined Congress' authority to define and declare war under the War Powers Clause. He focused on the original understanding of the Founders on the takings clause of the United States Constitution, also known as eminent domain in the United States. He wrote an article chronicling understanding of the scope of constitutional judicial review before Marbury v. Madison. He remains a prolific author of scholarly articles.
On June 6, 2006, he debated prominent classical liberal/libertarian law professor and published author Richard Epstein on the topic "Did Progressives Rewrite the Constitution?""With Walsh or Starr, the president and his supporters could more easily argue that a prosecutor was overzealous or irresponsible, because there had been a three-judge panel that appointed him. With Fitzgerald, you have a prosecutor who was appointed by the deputy attorney general [at the direction of the attorney general]. The administration almost has to stand behind him because this is someone they selected themselves. It is harder to criticize someone you yourself put into play."
"Few areas of constitutional law have produced as much heated debate as the war powers area, heat produced in no small part by the passionate belief that this is a subject of incalculable consequence. But, stunningly and ironically, there is little connection between the issues that scholars debate and the constitutional issues involving war that government officials and political leaders confront.
"The original understanding of the Takings Clause was, very simply, that the federal government had to compensate the property owner when it physically took property --such as when it took land to build a fort. The clause did not require compensation for regulations under any circumstances."
"Despite the public prominence of the property rights argument, there is actually nothing novel or particularly controversial about the conclusion that the Takings Clause was limited to physical seizures. With some notable exceptions, prominent legal scholars of all shades of political opinion—including such leading conservatives as former judge Robert Bork and former Solicitor General Charles Fried--support the conclusion that the property rights argument has no plausible foundation in the original understanding of the Takings Clause."
"[Fordham Law School is] pleased to rank in the top five [in placing graduates at the most successful firms]. We focus our education on practicing the law as well as knowing the law, so firms have come to realize that our graduates are prepared to work effectively right from the start. And our location in Manhattan within walking distance of many of the country's elite firms assures that there are exceptional opportunities available for students."
"This is a time of change for legal practice. The change in the economy precipitated changes that would have come inevitably…It does cause us to rethink how we prepare lawyers."
"Georgetown is a law school with incredible strength, so both in the first year and longer term, what I see as my mission is to build on those strengths. We’ll be focusing on experiential learning, externships and increasing opportunities in those areas. We’re going to be focusing on the academic depth and intellect strengths of the law school and continue to build on that with new hires. I consider myself incredibly privileged to be here at this moment."
"Against Textualism", 103 Northwestern Law Review 983 (2009)
"Taking Text Too Seriously", 106 Michigan Law Review 487 (2007)
Judicial Review before Marbury. 58 Stanford Law Review 455-562 (2005) [reprinted Fordham Law School Legal Studies Research Paper Series No. 85]
"Deans and Stories: Leading Minds. 36 The University of Toledo Law Review 207-211 (2004).
The War Powers Outside the Courts, in Mark Tushnet ed. The Constitution in Wartime, 143-160. Durham, N.C.: Duke University Press, 2005
Lochner’s New Millennium: Copyright Term Extension, Constitutional Law, and Eldred v. Ashcroft, 112 Yale L.J. (2003) (with Paul Schwartz)
The New Privacy, 101 Mich. L. Rev. 2163 (2003) (with Paul Schwartz) (book review)
Jam for Justice Holmes: Reassessing the Significance of Mahon, 86 Georgetown Law Journal 813 (1998)
Independent Counsel and Vigorous Prosecution and Investigation, 61 Law and Contemporary Problems 149 (1998)
The Armstrong Principle, the Narratives of Takings, and Compensation Statutes, 38 William & Mary Law Review 1151 (1997)
Learning from Lincoln, 65 Fordham Law Review 1781 (1997)
Fame, the Founding, and the Power to Declare War, 82 Cornell Law Review 695 (1997)
The Original Understanding of the Takings Clause and the Political Process, 95 Columbia Law Review 782 (1995)
The Case of the Prisoners and the Origins of Judicial Review, 143 University of Pennsylvania Law Review 491 (1994)
Prospective Overruling and the Revival of “Unconstitutional” Statutes, 93 Columbia Law Review 1902 (1993) (with Gene Sperling)
Taking the Framers Seriously, 55 University of Chicago Law Review 1016 (1988) (review of Walter Berns, Taking the Constitution Seriously (1987))
Note, The Origins and Original Significance of the Just Compensation Clause of the Fifth Amendment, 94 Yale Law Journal 694 (1985)