A federal appeals court on Tuesday ruled that the Trump administration can for now continue returning Central American migrants to Mexico while their requests for asylum in the U.S. are adjudicated, a boost for White House efforts to tighten the southern border.

The decision by the San Francisco-based Ninth U.S. Circuit Court of Appeals is a surprise victory for the administration, which previously had been on the losing end of several immigration-related rulings by the liberal-leaning court.

The...