[4] Born in Butte, Montana,[1][2] to John and Joan Morris, Brian Morris graduated from Butte Central Catholic High School, where he was an All-State athlete who competed in football, track, and basketball.

[1][2][4][10][11][6] After completing law school, Morris was a law clerk to Judge John T. Noonan, Jr. of the United States Court of Appeals for the Ninth Circuit and then to United States Supreme Court Chief Justice William Rehnquist.

[1][2][10][6] Morris is the only member of the Montana State Bar to have been a Supreme Court law clerk.

[6][12] In 1995, he joined the Iran – United States Claims Tribunal at the World Court, The Hague, Netherlands, to be a legal assistant.

The vacancy, in Great Falls, was caused by Judge Sam E. Haddon assuming senior status.

[14] His nomination was reported to the floor by the United States Senate Judiciary Committee on September 19, 2013.

[19][20] In 2010, he wrote the 4–1 decision in Wilson v. Montana that denying an inmate the use of a particular mental illness medication did not violate the criminal's rights.

[21][22] Indigenous Environmental Network and North Coast River Alliance, and Northern Plains Resource Council vs. United States Department of State and TransCanada Keystone Pipeline and TransCanada Corporation[23] In November 2018 Morris issued an order to stop the construction of the Keystone XL Pipeline so that further research could be done on its environmental effects.