When India and Pakistan became independent states in 1947, each inherited a bristling minority problem. Twelve million apprehensive Hindus stayed in Pakistan; 43 million Muslims stayed in India. The Indian Parliament guaranteed its minorities equality, and Prime Minister Nehru conspicuously appointed Muslims and Christians to his Cabinet. But Pakistan, in framing its own constitution, chose the dark path which might lead to theocracy and fear. The Constituent Assembly ruled that the nation should become “the Islamic Republic of Pakistan” (presumably within the British Commonwealth, like India)

Pakistan became independent of the United Kingdom in 1947, but remained a British Dominion like Canada or Australia until 1956. Under Section 8 of the Indian Independence Act, 1947, with certain adaptations, served as the working constitution of Pakistan, but the need of a full independence and a constitution to be framed by the elected representatives of the people was all the more necessary for the free citizens of a sovereign state. Since India became a republic in 1950, the feeling had increased that Pakistan should assume the same special status that India felt she had attained. Republican sentiment had almost certainly been further strengthened by what many Pakistanis consider Britain’s failure to support her openly in the Kashmir dispute. Even so, Pakistan had no present intention of dissociating herself from the Commonwealth. A proposal to do so was quietly dropped.

There was no indication of what precisely the term ‘Islamic Republic’ would mean, but the leader of the Hindu members of the Constituent Assembly, who walked out in protest, had already labelled it as.” an attempt to make Pakistan a theocratic State,” in which Hindus (13 per cent of the population) would be placed on a separate electoral rolls, denied the highest office of State, and forced into a position of inferiority. Certainly it would not help to solve the problem of the Hindus of East Bengal, nor improve relations with India.

Pakistan was the first country to become Islamic Republic, followed by Mauritania, Iran and Afganistan over a period.

Reference:

http://www.historyorb.com/day/november/2

http://content.time.com/time/magazine/article/0,9171,819249,00.html

http://archive.spectator.co.uk/article/6th-november-1953/4/the-islamic-republic-of-pakistan

http://en.wikipedia.org/wiki/Islamic_republic