A federal appeals court upheld California’s 10-day waiting period for gun purchases on Wednesday, in one of the first rulings to consider whether the Second Amendment allows authorities to make buyers wait to take home their new firearms even after they have passed a background check.

The Ninth U.S. Circuit Court of Appeals in San Francisco held that people who already own guns and those with a permit to carry a concealed firearm were still​ subject​ to the state’s “cooling off” period.

The...