"Why are we invited and not be afforded a chance to ask questions?" asked one of the mineworkers from Marikana, who was wearing a green Association of Mineworkers and Construction Union (Amcu) T-shirt.
"Hold on [with] the music," he called out, after it was announced that Johnny Clegg would perform at the lecture on Thursday.
The group asked what Manuel had done as a former finance minister to close the gap between the rich and the poor.
Claire Ceruti, of the Democratic Left Front, led the group as it was escorted from the hall by security.
"We want answers. What have you done?" she shouted.
Earlier, the group held posters outside the hall asking Manuel whether the Cabinet had ordered the police to kill protesting mineworkers at Marikana last year.
The police opened fire on striking mineworkers, killing 34 of them while trying to disperse a group gathered on a hill near Lonmin's platinum mine in Marikana on August 16. In the preceding week, 10 people died, among them two police officers and two security guards.
The circumstances surrounding the deaths are being investigated by the Farlam commission of inquiry.
Social, economic justice
"Trevor Manuel, was your Cabinet behind the decision to fire on Marikana with live ammunition," read one poster.
Manuel was the university to deliver the Ruth First memorial lecture.
The Democratic Left Front said First had been a fighter for social and economic justice.
"She would have been horrified by the massive inequality in the mining sector, the crippling low wages earned by platinum mineworkers, who risk life on a daily basis to supply the mineral that are so important to the South African economy," said Samuel Ngece.
Manuel said the revolt by Marikana mineworkers was a result of inequalities.
"As a country, South Africa must learn from the Marikana incident. It must be a wake-up call," he said.
Manuel said that according to a census report, 40% of people in Marikana lived in informal backyard rooms. Most of them were indebted to more than one loan shark.
"The inequality of apartheid has denied black South Africans a share in the economy," he said.
Injustices of the past
The government needed to intervene to address the injustices of the past, Manuel said, adding: "We need a people-centred democracy."
He said the National Development Plan was intended to address the inequalities of apartheid.
"There is a better tomorrow. A better tomorrow that requires sacrifice from all."
He said Ruth First had strived for equality and had died fighting inequality.
First was an anti-apartheid activist who was born in Johannesburg in May 1925. She was killed by a parcel bomb addressed to her in exile in Mozambique in August 1982.
Her parents, Julius First and Matilda Levetan, immigrated to South Africa from Latvia as Jewish immigrants in 1906 and became founder members of the Communist Party of South Africa, the forerunner of the South African Communist Party. – Sapa