On February 12, 2003, Callahan was nominated by President George W. Bush to serve on the United States Court of Appeals for the Ninth Circuit.

On October 9, 2005 Chicago Sun-Times columnist Robert Novak reported Callahan was one of two finalists for the O'Connor seat, the other being White House Counsel Harriet Miers, whom Bush nominated.

On November 13, 2023, Callahan voted against temporarily blocking Idaho's abortion ban despite to its lack of exceptions for medical emergencies.

[8] On July 14, 2014, Callahan was presented the Ninth Circuit Professionalism Award from the American Inns of Court.

The award presentation occurred at the Ninth Circuit Judicial Conference in Monterey, California, and was presented by Dean Deanell Reece Tacha of the Pepperdine University School of Law; Dean Tacha was a retired judge of the United States Court of Appeals for the Tenth Circuit and current President of the American Inns of Court Foundation.