Mallet had wide experience of foreign politics in general; and, in Sir Edward Grey's opinion, a special knowledge of the problems to be dealt with by a British Ambassador to the Porte.
Britain and Germany had both helped with the settlement after the First Balkan War and relations with the Ottoman Empire were comfortable.
By the time Mallet reached his post, three weeks after the outbreak of war, the question of Turkey's affiliation was practically decided, although the Allied powers continued to negotiate with the Porte until the Ottomans joined the war on the side of the Central Powers, when Mallet and other Allied ambassadors had to leave Constantinople.
Mallet was criticised at the time and afterwards for failing to keep the Ottoman Empire out of the war, but Germany's influence was aided by Turkey's long-running enmity with Russia, one of the Allies.
In 1912 Mallet acquired the dilapidated 14th century Otham Manor, then known as Wardes, having 'detected amid the ruin and squalor the possibility of restoring an exceptionally fine old timber house to something like its pristine beauty'.