[2][3] Pregerson was a United States Marine Corps First Lieutenant in World War II, during which he was severely wounded in the Battle of Okinawa (4 May 1945).

[5] Pregerson was nominated by President Jimmy Carter on August 28, 1979, to the United States Court of Appeals for the Ninth Circuit, to a new seat created by 92 Stat.

[5] At his confirmation hearing, Pregerson told the United States Senate Committee on the Judiciary that "My conscience is a product of the Ten Commandments, the Bill of Rights, the Boy Scout Oath, and the Marine Corps Hymn.

He wrote the majority decision in the Ninth Circuit panel on Gonzales v. Raich, holding that the Interstate Commerce Clause forbade the federal government from interfering with state laws that permitted the use of medical marijuana.

[10] The ruling was later overturned by the Supreme Court, however, which held that it is within Congressional power to regulate intrastate activities that are seen to influence interstate commerce, including using homegrown marijuana for medical purposes.

[11] In the case United States v. Reynard, the circuit court upheld the DNA Analysis Backlog Elimination Act of 2000.

[12] Pregerson wrote a dissenting opinion in Jespersen v. Harrah's Operating Co., which was joined by judges Alex Kozinski, Susan P. Graber, and William A. Fletcher.

The majority ruled that Jespersen had not shown sufficient evidence that Harrah's "Personal Best" policy, which required women but not men to wear makeup, was sex discrimination.

The prosecution argued that Zaugh had violated the Selective Service Act by refusing to report for a preinduction physical examination and military induction during the Vietnam War.

The prosecution presented evidence from Zaugh's Selective Service file, emphasizing that he had been given clear instructions and opportunities to comply with the draft process.

[14] After hearing both sides, Pregerson acquitted Zaugh of the more serious charge of refusing induction but found him guilty of failing to report for the physical examination.

Instead, he sentenced Zaugh to two years of probation with the condition that he perform civilian work contributing to national health and safety.

In 2001, the Department of Veterans Affairs honored him and the then-Acting Secretary Hershel Gober and presented Pregerson with a token of appreciation with the VA seal.