[2] From 1966 until 1968, he was State Counsel to the Republic of Botswana, sponsored by an Africa-Asia Public Service Fellowship, where he drafted a codification of tribal law and was the country's principal prosecutor in the regular (non-tribal) criminal courts.
In 1975 he returned to private law practice with the New York firm of Carter, Ledyard & Milburn, where he was a partner in commercial litigation.
[2] In 1981 Walker became Assistant Secretary of the Treasury, responsible for policy in law enforcement, regulatory, and trade matters, and with oversight of the Customs Service, Secret Service, Federal Law Enforcement Training Center, Bureau of Alcohol, Tobacco and Firearms, and the Office of Foreign Assets Control.
Among the shortcomings of the Secret Service that the review identified and remedied were inadequate reserve personnel and the use of unencrypted radio communications.
His work caught the attention of New York Senator Alphonse D'Amato who supported him for the position of district judge.
As a district judge, Walker presided over a variety of civil and criminal proceedings, including notably the 1989 tax fraud trial of billionaire hotel magnate Leona Helmsley, whom he sentenced to four years in jail.
[3] Walker was nominated by President George H. W. Bush on September 21, 1989, to a seat on the United States Court of Appeals for the Second Circuit vacated by Judge Irving Kaufman.
"[6] An independent judge, in his view, is one who faithfully applies existing law to the facts of the case at hand, giving due respect to precedent,[6] and resists the temptation to effectively rewrite legislative enactments.
From 1996 to 2000, Walker was an adjunct professor at New York University School of Law and a member of NYU's Institute of Judicial Administration and Appellate Judges Seminar.
Walker is actively involved in initiatives to promote the rule of law, strengthen judiciaries and foster cooperation among judges around the world, especially in Eastern and Central Europe, China and the Middle East.
[7] Walker has worked across Central and Eastern Europe to promote the development of judicial institutions in individual countries and to foster collaboration among judiciaries across the region and the United States.
Chief Justice of the United States John G. Roberts, Jr. delivered the opening remarks and participated in the first conference.
He then led the roundtable discussions on judicial integrity among the heads of the Supreme Court in the region at the CEELI Institute in Prague in 2007 and 2010.
He helped plan and participated in subsequent Chief Justice Conferences hosted in Albania (2012), Montenegro (2013), Georgia (2014), Croatia (2015), Serbia (2016), Hungary (2017), Lithuania (2018) and Slovakia (2019).
He has discussed legal reform issues with Presidents Alfred Moisiu and Bamir Topi and prime ministers Fatos Nano and Sali Berisha.
In 2009, working with China law expert professor Jerome Cohen and other American scholars and judges, Walker led the American delegation at the inaugural Sino-American Dialogue on the Rule of Law and Human Rights, a Track II dialogue co-sponsored by the National Committee on U.S.-China Relations and the China Foundation for Human Rights Development, in Nantong[19][20][21] and thereafter in other venues.
He has conferred with the Chief Justice of the Supreme Court of Iraq, Medhat al-Mahmoud, on issues relating to the rule of law and human rights.
On the evening of October 17, 2006, while driving home, Walker's Ford Escape automobile struck a police officer, Daniel Picagli, who was directing traffic in a rainstorm at a road construction site for AT&T in New Haven, Connecticut.