[2][4] He began his career as an associate at the law firm of Landels, Ripley & Diamond in San Francisco, California, where he worked from 1991 to 1995.

[3] In 2000, Watson returned to private practice, joining the law firm of Farella Braun + Martel LLP, where he worked on product liability, toxic tort, and environmental cost recovery litigation.

[3] From 1998 to 2006, Watson served in the United States Army Reserve in the Judge Advocate General's Corps, honorably discharged with the rank of captain.

[6] Watson was rated "well qualified" by a substantial majority of the American Bar Association's Standing Committee on the Federal Judiciary.

[14] On June 12, 2017, the U.S. Court of Appeals for the Ninth Circuit upheld the majority of the injunction, unanimously determining that Trump had "exceeded the scope of authority delegated to the president" under the Immigration and Nationality Act.

The State of Hawaii filed an emergency motion to clarify the scope of "close familial relationships" under the terms of the injunction and Supreme Court decision narrowing it, asking the district court to rule "that the federal government may not enforce the controversial bans against fiances, grandparents, grandchildren, brothers-in-law, sisters-in-law, aunts, uncles, nieces, nephews and cousins of people currently living in the United States.

[19] Subsequently, the Ninth Circuit ruled that Watson "had the authority to interpret the Supreme Court's order and block any violation of it" and the issue returned to him.

He ordered that the definition of "close family members" be expanded to include grandparents, grandchildren, brothers-in-law, sisters-in-law, aunts, uncles, nieces, nephews, and cousins in the United States.

"[21] On October 17, 2017, Watson again issued a temporary restraining order preventing a later revision of Trump's travel ban from going into effect.