Born in Bochum, Province of Westphalia, his career in the Imperial German Armed Forces began in 1897, when he became a cadet in a military school, he retired after the Second World War as one of the most decorated Generals of the former Luftwaffe.

When the First World War begun in August 1914, Hauptmann Alfred Keller was serving in a Western Front bomber unit Kagohl 5, Kampfstaffel (Kasta) 27, with which he would fly his first combat missions.

Keller participated in the first air reconnaissance mission of Paris in October 1914, which served to obtain evidence in the absence of anti-aircraft defences in the French capital.

On the Verdun and Somme fronts Keller performed some missions of reconnaissance and offensive patrolling, which led to him in September 1915 being nominated Kommandeur of Kagohl 7, Kampfstaffel (Kasta) 40, a unit that he would help to consolidate in the following months.

On the night of 30–31 January 1918 Keller, in spite of the fierce anti-aircraft opposition, again attacked Paris, causing a great panic in the civilian population, the pilots of Bogohl 1 returned safely though.

Here he began, as a means of resistance to Allied conditions of Armistice the secret training of new military pilots, and he would be one of the first men called by Hermann Göring to help in the reconstruction of the Luftwaffe, as soon as the Nazis had assumed power in 1933.

With the organisation of the Luftwaffe, Keller was commissioned with the rank of Oberst (Colonel), and assumed the command of the first bomber squadron, during the winter of 1936, KG 154 “Boelke” (He 111B-1).