Dr Waseem bagged 181 of the total 351 votes cast, whereas, Ahsan's tally stood at 169; one vote was rejected.
The seat had become vacant when PTI’s Chaudhry Mohammad Sarwar resigned before taking charge as the governor of Punjab.
Several members of the opposition parties complained that the election was allegedly rigged by closing the door for entry of the members of opposition parties but keeping the entrance open for members of treasury benches.
"I was in the assembly, our door was closed but the other door was kept open," said PML-N's Waris Kallu. "Rigging was done in front of us. Today reminded us of July 25."
PML-N leader Uzma Bukhari claimed that the "Punjab chief election commissioner misused his authority" and demanded his "immediate sacking".
Later, Dr Waseem thanked Prime Minister Imran Khan for putting his faith in him.
"I also thank our allies who voted for me," he said. "I will fight Punjab's case in the Senate with full force, and will work for the public's better future."
Dr Waseem is a senior PTI member and has served as an adviser to Imran Khan on foreign political parties’ relations. He was elected senator on the PML-Q ticket from 2002 to 2008 and later served as minister of state for interior in former prime minister Shaukat Aziz’ cabinet during the military regime of retired Gen Pervez Musharraf.
PTI's provincial minister Aleem Khan rejected the PML-N's claim that his party received fewer votes than it should have.
"Our votes have not decreased," he said. "A PTI and another PML-Q member were outside the country, and one of our votes was rejected."
