Following graduation from high school, Siglienti began to work at a local bank in Sassari. He took part in
World War I as a
second lieutenant and was decorated by the
King of Italy in July 1918 due to his activities in the war. He was one of the founders of the
Action Party in Sardinia.{{cite encyclopedia|title=Sigliènti, Stefano|encyclopedia=
Treccani|language=it On 19 November 1943, Siglienti was arrested by the
Schutzstaffel and was kept in the
Regina Coeli prison. He managed to escape from the prison through the assistance of his wife, Ines, who had also been involved in the clandestine struggle against
Fascist Italy. Therefore, Siglienti was saved from being one of the victims of the
Ardeatine massacre that would take place a few days later on 24 March 1944. He was appointed minister of finance in June 1944 to the cabinet led by
Ivanoe Bonomi and was in office until December 1944. From 1 March to 10 December 1945, Siglienti worked as the commissioner of the
Banca IMI and then became its president. That same year, he was also named a member of the
National Council. In addition, he was appointed president of the
Italian Banking Association, in September 1945 a position that he held until 1971.{{cite journal|author=Sandro Gerbi ==Personal life and death==