Olgiati studied in Chur and Bern. He studied mathematics and physics at the ETH Zurich. He met Leonhard Ragaz. From 1929 to 1932, he was a teacher at the Odenwaldschule in Heppenheim. In 1933, he worked at Faithfull's home for educators in England. From 1934 to 1935, he worked for Fritz Wartenweiler in the youth courses. In 1935 he became secretary of the Service Civil International. During the Spanish Civil War, in February 1937, he worked for the rescue of vulnerable children and founded the Swiss Working Group for Spanish Children (SAS) with Fritz Wartenweiler and Regina Kägi-Fuchsmann. 