Zulifqar Ali Bhutto introduced a new constitution in Pakistan on August 14, 1973.
According to the 1973 constitution, both the national assembly and senate elect a president for Pakistan whereas the prime minister is selected by the national assembly.
The Bicameral Legislature system was introduced for the first time in Pakistan in the constitution of 1973.
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1956 Constitution
March 23, 1956 by PM Chaudhry Mohammad Ali + GG Iskander Mirza