Hentig joined the Imperial German diplomatic service in 1909 and was posted as an attaché to the German mission at Beijing. He was later posted to Istanbul and Tehran. During the First World War he was wounded in the Battle of the Masurian Lakes, then later in 1915, with Oskar Niedermayer, led the Niedermayer–Hentig Expedition, a German mission to Kabul that sought to enlist the Afghan Amir's support for the Central Powers and an attack on British India.