He was an editor of the Journal of Agriculture "Grüne" from 1936 to 1941 and organized a suitable pavilion in Landi in 1939.
During the Second World War, he was responsible of the Swiss program to reduce food imports and increase agricultural production, which consisted mainly in extending the cultivation area, and reducing meat production in favour of cereals production. The program was called after his name, as Wahlen Plan.
From 1943 to 1949 he was a professor of Agronomy at ETH in Zurich. In 1949 he was appointed the director of the department of Agriculture to the FAO (Food and Agriculture Organization of the United Nations).
He was President in 1961 and Vice President in 1960. His testament is preserved in the Swiss Federal Archives in Bern and in the Archives of Contemporary History at the ETH in Zurich.
Several times he represented the Federal Council abroad.