In 1984, Mosman clerked for
Malcolm Richard Wilkey, judge on the
United States Court of Appeals for the District of Columbia Circuit. After leaving Powell's employ, Mosman entered private practice in
Portland, Oregon, in 1986 at Miller Nash (now
Miller Nash Graham & Dunn).
Federal judicial service On May 8, 2003, President
George W. Bush nominated Mosman to serve as
United States district judge of the
United States District Court for the District of Oregon to the seat vacated by
Robert E. Jones, who assumed
senior status on May 1, 2000. On September 25, 2003, he was confirmed by the
United States Senate by a 93–0 vote. He received his commission on September 26, 2003. He served as Chief Judge for approximately 4 years from February 1, 2016, to December 23, 2019. He assumed
senior status on December 27, 2021. Mosman had issued the temporary injunction in December 2007 to prevent
Oregon's new civil union law from taking effect in January. This was in response to a legal challenge by a group that had attempted to place a referendum on the November 2008 ballot to block the civil union law that had been passed by the
Oregon Legislative Assembly. The legal issue centered on how the
Oregon Secretary of State verified signatures on petitions. The heavily redacted, 412-page application cites many sources, including confidential informants. Among those many sources, the application cites the
Steele dossier, leading a legal commentator to criticize the basis of the warrant.
Kawhi Leonard v. Nike Inc In April, 2020, Mosman granted
Nike's motion dismissing
Kawhi Leonard's copyright claims over a disputed logo, writing ::"It's not merely a derivative work of the sketch itself...I do find it to be new and significantly different from the design."
Oregon restraining order against Department of Homeland Security (2020) In July 2020, the Oregon Attorney General,
Ellen Rosenblum, requested a restraining order based on the detainment actions of Department of Homeland Security and Customs and Border Protection personnel. The AG alleged that unmarked federal agents had unlawfully detained protesters in
Portland without probable cause. Mosman rejected the request for a restraining order, stating that "because it has not shown it is vindicating an interest that is specific to the state itself — I find the State of Oregon lacks standing here and therefore deny its request for a temporary restraining order".
Miss America In 2021, Mosman dismissed a lawsuit challenging the
Miss United States of America pageant's rules that dictate that their contestants be “natural females.” ==Recognition==