Member National Assembly Shafiq Arain was the first person to cast the vote.
Polling is being held on thirty-seven vacant seats of the Senate.
All the eleven candidates for Senate from Punjab have already been elected unopposed while candidates from Sindh, Balochistan, Khyber Pakhtunkhwa and Federal Capital will be elected today.
Two senators will be elected from the federal capital, eleven from Sindh and twelve each from Balochistan and Khyber Pakhtunkhwa.
It merits a mention here that fifty-two senators in the house of 100 are set to retire on 11th of this month after completion of their six-year term.
Other prominent figures who have cast their votes so far include Foreign Minister Shah Mahmood Qureshi, Deputy Speaker National Assembly Qasim Khan Suri, Interior Minister Sheikh Rasheed Ahmad, Minister for Communications Murad Saeed, Minister for Science Fawad Chaudhary and Minister for Water Resources Faisal Vawda.