During World War II, Kristofer Kluge actively participated in the MILORG resistance movement until he was arrested and sent to Grini, where he was incarcerated until the end of the war. The practice of law gradually resumed starting in the summer of 1945.
During the postwar era, the firm was engaged in cases concerning property law. In the 1950s, Parr started his own firm, and Kristofer Kluge eventually established a partnership with Per Riis. In 1955, Kristofer's son, Thor Kluge, joined the firm as a lawyer and partner.
In 1965, Kristofer Kluge started to gradually scale back, and Thor Kluge continued on his own from 1970. In 1980, Odd-Sverre Rage and Clement Endresen entered the firm as partners.
In the 1980s, the firm expanded substantially, both locally in Stavanger and in Oslo. The Stavanger office moved to Forus, and Harald S. Kobbe and Stig Tufte-Johnsen started the Oslo office in 1987. The Bergen office was established in 1994. After a few name changes, a decision was made to use the name Kluge.