[2] He joined Nasjonal Samling in 1933, and was appointed commander of Infantry Regiment 15 the same year.
[1] When the Germans invaded Norway 9 April 1940, Sundlo held the rank of colonel and was commander-in-chief for Narvik area.
[2] When the Norwegian fascist leader Vidkun Quisling visited Adolf Hitler in Berlin in the autumn of 1939, he had shown the German Führer a letter sent to him by Sundlo, and described the latter as pro-German.
After that he served as the collaborationist county governor of Oslo and Akershus from 1943 to 1944 and lastly in Sogn og Fjordane until the end of the war.
[1][2] After the surrender of Narvik on 9 April 1940, Sundlo was accused of treason by his divisional commander, General Carl Gustav Fleischer.