Jonas first entered politics as a young adult while he was working as a typesetter, joining the Socialist Youth Movement and the Printers' Union.

He served on the town council of Floridsdorf beginning in 1945 and was then placed in command of Vienna's food supply and housing in 1948 and 1949, respectively.

As president, he oversaw the creation of a minority government under Bruno Kreisky, the leader of the Socialist Party.

Viennese Workers' Education Centre) where his instructors included fellow future presidents Karl Renner, Adolf Schärf, and Theodor Körner.

[3] Jonas became mayor of Vienna in June 1951 as the previous office holder, his former instructor Körner, became president of Austria.

As mayor, Jonas also served the chairman of the Austrian union of towns and an executive within the Council of European Municipalities and Regions.

[2] President Adolf Schärf of the Socialist Party of Austria (SPÖ) died in office, prompting a presidential election in 1965.

[5] In 1966, Jonas was awarded the Grand Cross of The Royal Norwegian Order of St. Olav with Collar, and in 1969 the ÖOC Pierre de Coubertin Medal.

[5] Jonas was popular among the public, to the point that SPÖ party leader Bruno Kreisky tried to make their names synonymous during the 1970 legislative election.

The SPÖ held a plurality and Kreisky asked Jonas to appoint a minority government with the implicit endorsement of the Freedom Party of Austria.

[5] Continuing his interest in international affairs, Jonas visited Iran in 1965, the United Kingdom in 1966, Thailand and Canada in 1967, Yugoslavia in 1968, Switzerland and Romania in 1969, Belgium, Bulgaria, and Hungary in 1970, Finland in 1972, and West Germany in 1973.