Clifton received an Artium Baccalaureus degree at Princeton University and a Juris Doctor from Yale Law School.

He was nominated to the United States Court of Appeals for the Ninth Circuit by George W. Bush on September 4, 2001 to fill a seat vacated by Cynthia Holcomb Hall.

[5] On February 7, 2017, Clifton along with fellow Ninth Circuit judges William Canby and Michelle Friedland heard oral arguments on a motion from the Trump administration to stay the temporary restraining order in State of Washington v. Trump, part of the ongoing court cases related to Executive Order 13769.

[9][10] In July 2018, Clifton dissented when the court found that Hawaii's licensing requirement to openly carry firearms violated the Second Amendment to the United States Constitution.

N. Randy Smith issued a dissent, and on July 26, the Supreme Court overturned Friedland and Clifton by a 5-3 vote on ideological lines with Stephen Breyer saying he would temporarily block the construction of the wall but allow funding to be set aside for it.