Polling to elect the new chairman and his deputy was held in the parliament building.
Presiding Officer Sardar Yaqoob Khan Nasar announced the result of contest for chairman after all senators had cast their vote.
Muhammad Sadiq Sanjrani got 57 votes against Raja Zafarul Haq (of PML-N) and has been elected as chairman, said Nasar.
Sanjrani from Balochistan province was supported by the Joint Opposition, including Pakistan Peoples Party (PPP), Muttahida Qaumi Movement-Pakistan (MQM-P), Pakistan Tehreek-i-Insaf and independents from Balochistan and the Federally Administered Tribal Areas.
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The process to elect the deputy chairman was going on. Tough competition is expected between Saleem Mandviwalls of PPP, who is supported by opposition and Usman Kakar of Pakhtunkhwa Milli Awami Party's (PkMAP), an ally of the ruling party.
Earlier, 51 newly elected senators took oath to become member of the Senates.
Only former Finance Minister Ishaq Dar was not present to take the oath as he was away in London due to poor health.
Krishna Kumari Kolhi today scripted history when she was sworn-in as Pakistan's first-ever Hindu Dalit woman Senator. Her arrival was a spectacle as she reached the parliament house with her family in traditional Thari dress, a trademark of Tharparker district of Sindh province.
The strength of the house reduced to 103 from 104 due to absence of PML-N senator-elect Ishaq Dar, who is in London for medical treatment. Hence, winner needs 52 votes.
Initial surveys, media reports and announcement by the PML-N leaders suggested that Haq will win by thin margin but in the end he lost by a big margin.
The political parties were scrambling till last minute to get the upper hand through election of chairman.
Earlier, PPP chairman Bilawal Bhutto Zardari announced to support independent Sadiq Sanjrai, while fielding Mandiviwalla as deputy chairman.
Earlier, Presiding Officer Sardar Yaqoob Khan Nasar said the election for chairman and deputy chairman would take be held at 4pm in the parliament house.