On July 17, 1973, Khan seized power from his cousin King Zahir and proclaimed Afghanistan a republic.
Khan was known for his progessive policies especially in relation to the rights of women and for initiating two five-year modernization plans (1956 - 1961 and 1962 - 1967) when he served as Prime Minister under King Zahir and a seven-year plan in 1976 when he was President. Much of the aid for these plans came from the Soviet Union.
Khan and most members of his family were assassinated on April 28, 1978 a day after the commencement of the Marxist revolution that established the Democratic Republic of Afghanistan.