He worked in Stavanger Aftenblad from 1929 to 1945, except for the World War II years during parts of which he was imprisoned, and then in Verdens Gang from 1945.
He was a nephew of Jakob Hveding Sletten and a maternal grandson of Christopher Bruun.
Nazification attempts of the press soon began, and when a member of the Fascist party Nasjonal Samling was installed in Stavanger Aftenblad in 1941, Sletten quit his job.
He was then detained in Berg concentration camp until the liberation of Norway, which incidentally took place on his birthday.
[3] After the war, Sletten returned to his old job in Stavanger Aftenblad, but quit after a few months, following a dispute over the appointment of Christian S. Oftedal as editor-in-chief.
Sletten replaced founding editor Christian A. R. Christensen, and co-edited with Oskar Hasselknippe, who had held the position since 1953.
[4] During Sletten's period as editor Verdens Gang developed into one of Norway's leading newspapers, more or less trebling its circulation.