Following World War II and the end of Japanese rule, Chang plunged into politics in 1946 and was elected to the National Assembly in May 1948. With the establishment of the ROK in 1948, President Syngman Rhee appointed Chang chief representative to the United Nations (UN). Chang went on to serve as South Korea's first ambassador to the United States from 1949 to 1951, during which time he tried to secure additional U.S. military assistance prior to the outbreak of the Korean War in June 1950.
In February 1951, Rhee appointed Chang premier. Chang resigned in 1952 and then joined the anti-Rhee faction, which organized the Democratic Party in 1955. Chang was elected vice president in 1956 but lost his reelection bid in March 1960.
The student uprisings of April 1960 brought the collapse of Rhee's government, while the subsequent National Assembly elections of 29 July 1960 gave birth to the ROK's second republic, a parliamentary system. Chang was inaugurated as its first premier in August 1960. Park Chung Hee's 16 May 1961 military coup overthrew Chang's government, however, making it the first and last parliamentary government in Korean history. Park subsequently banned Chang from political activities and had him imprisoned. After his release, Chang concentrated on religious activities. He died in Seoul on 4 June 1966.
Han, Sungjoo. The Failure of Democracy in South Korea. Berkeley: University of California Press, 1974.