He studied at the lukio in Mikkeli from 1935 until 1939, then was drafted into the army in the Winter War, serving in a radio reconnaissance unit.

After the Winter War ended, Karjalainen briefly continued his education at the Lutheran folk high school in Tuusula, but once the Continuation War broke out, he returned to his old radio reconnaissance unit, serving at listening stations in Petrozavodsk (Äänislinna) and Medvezhyegorsk (Karhumäki) in the Finnish-occupied Republic of Karelia.

It remained in office until December the following year; ultimately disbanding due to the resignations of ministers sympathetic to the SAK over economic and political issues.

In 1981 Karjalainen put his name forward to be presidential candidate of the Centre Party, but lost to Johannes Virolainen.

The later stages of Karjalainen's political career were notably affected by his alcoholism – a national scandal ensued following his final resignation as prime minister when he was arrested for drunk-driving in 1979 and his involvement in an alcohol-fuelled incident at a reception marking the 34th anniversary of the signing of the Finno-Soviet Treaty of 1948 in 1981.

Karjalainen's use of alcoholic beverages and the peculiar manner in which he spoke the English language led him to receive the moniker of "Tankero".

In 1986, Karjalainen was offered honorary membership of the Centre Party, but refused to accept the title on the basis of the treatment he had previously received.

However, the Constitutional Affairs Committee did not consider Väyrynen to have violated the Ministerial Accountability Act and the matter therefore lapsed.