|Judge of the United States Court of Appeals for the Ninth Circuit|
September 26, 1986
|Appointed by||Ronald Reagan|
|Preceded by||Robert Boochever|
|Born||Diarmuid Fionntain O'Scannlain
March 28, 1937
New York City, New York, U.S.
|Alma mater||St. John's University, New York
University of Virginia
Born in New York, New York, O'Scannlain received a B.A. from St. John's University in 1957, a J.D. from Harvard University in 1963, and an LL.M. from the University of Virginia School of Law in 1992. He was in the United States Army Reserve, JAG Corps from 1955–78.
In September 1960, O'Scannlain attended the founding conference of Young Americans for Freedom, held at William F. Buckley, Jr.'s estate in Sharon, Connecticut. At that conference O'Scannlain was elected to serve on YAF's original Board of Directors.
He was a tax attorney for the Standard Oil Company of New Jersey and New York City from 1963–65, and in private practice in Portland, Oregon from 1965 to 1969. He was a Deputy state attorney general of Oregon State Department of Justice from 1969–71, then an Oregon public utility commissioner from 1971–73, and finally Director of the Oregon Department of Environmental Quality from 1973–74.
Run for Congress
In 1974, O'Scannlain was the Republican candidate for the United States House of Representatives representing Oregon's 1st congressional district, but lost to Democrat Les AuCoin, the first time the district had ever elected a Democrat.
He returned to private practice in Portland from 1975–86, also working as a consultant to the Office of the President-Elect of the United States from 1980–81, and as a team leader for the President's Private Sector Survey on Cost Control ("Grace Commission") from 1982–83. He chaired an advisory panel for the U.S. Secretary of Energy from 1983–85.
Federal judicial service
On August 11, 1986, President Ronald Reagan nominated O'Scannlain to a seat on the United States Court of Appeals for the Ninth Circuit vacated by Judge Robert Boochever. O'Scannlain was confirmed by the Senate on September 25, 1986, and received his commission on September 26, 1986. On September 26, 2016, the thirtieth anniversary of his appointment, he notified President Obama of his intention to take senior status effective December 31, 2016. 
O'Scannlain is a strong supporter of splitting the Ninth Circuit.
In a controversial March 2010 case, O'Scannlain joined the majority opinion that Seattle police officers did not employ excessive force when they tasered a pregnant woman. He was joined by Judge Cynthia Holcomb Hall in a contested 2–1 decision (judge Marsha Berzon dissented).
On February 13, 2014, O'Scannlain wrote the opinion for the majority in the case of Peruta v. San Diego, and issued a ruling that stated California's may-issue concealed carry rules, as implemented by the County of San Diego, in combination with a ban on open carry in most areas of the state, violate the Second Amendment, because they together deny law-abiding citizens the right to bear arms in public for the lawful purpose of self-defense. Consuelo María Callahan joined him in the majority, while Sidney Runyan Thomas dissented.
- Lat, David (29 September 2006). "Congratulations, Judge O'Scannlain!". Above the Law. Retrieved 14 February 2014.
- M. Stanton Evans, Revolt on the Campus (Chicago: Henry Regnery Co., 1961), 109–10.
- "New Faces, New Strains". Time. 1974-11-18. Retrieved 2009-06-19.
- "Ninth Circuit Judge Diarmuid O’Scannlain to Assume Senior Status" Public Information Office, United States Courts for the Ninth Circuit, September 26, 2016
- "20 Questions for Circuit Judge Diarmuid F. O'Scannlain of the U.S. Court of Appeals for the Ninth Circuit". law.com.
- Josh Wolf v. United States Ninth Circuit
- David Kravets: Court OKs Repeated Tasering of Pregnant Woman – Wired News Threat Level column, 29 March 2010
- Dolan, Maura, and Perry, Tony (February 13, 2014). "Court Overturns Restrictions on Concealed Guns in Much of California", Los Angeles Times. Retrieved February 14, 2014.
- Diarmuid O'Scannlain at the Biographical Directory of Federal Judges, a public domain publication of the Federal Judicial Center.
- Appearances on C-SPAN
|Judge of the United States Court of Appeals for the Ninth Circuit