In 1915, Lilliehöök was appointed head of the Royal Swedish Army Staff College and two years later, in 1917, he was promoted to colonel in the General Staff and appointed regimental commander of the Jämtland Ranger Regiment. From April to May 1917, Lilliehöök conducted military studies at the Carpathian Front in Austria. In 1921, Lilliehöök joined the Norwegian Army and in 1928 he was promoted to major general in the Swedish Army and appointed military commander of Upper Norrland's Troops. He conducted military studies in Finland in 1929 and in 1930 he was appointed commanding officer of the Eastern Army Division (Östra arméfördelningen) and Commandant General of Stockholm Garrison. In 1934 he was promoted to lieutenant general and he conducted military studies in Northern Norway in 1935. Lilliehöök retired in 1936. Four years later, Lilliehöök again served as Commandant General of Stockholm Garrison but only for a few months, from April to December 1940.
