After graduation in mathematics in 1912, Väisälä worked for the Finnish Meteorological Institute in aerological measurements, specializing in the research of the higher troposphere.

In 1917 he published his dissertation in mathematics Ensimmäisen lajin elliptisen integralin käänteisfunktion yksikäsitteisyys (The single-valuedness of the inverse function of the elliptic integral of the first kind).

[1] His dissertation was the first and still is the only mathematical doctoral thesis written in the Finnish language.

[2] Väisälä participated in development of radiosonde, a device attached to a balloon and launched to measure air in the higher atmosphere.

During the World Congress of Esperanto of 1969, which was held in Helsinki shortly before his death, he served as the rector of the so-called Internacia Kongresa Universitato ("International Congressual University"), and coordinated the specialistic lectures in Esperanto given by various academicians to the congressists.