"The tragedy has to be approached as a collective failure by many role players. I don't think that many can say they do not bear any form of responsibility," he told the commission's public hearings in Pretoria.
Ramaphosa was being cross-examined by Dali Mpofu, for the wounded and arrested Marikana miners.
Ramaphosa was a non-executive director and shareholder of Lonmin at the time.
"The responsibility has to be collective. As a nation, we should dip our heads and accept that we failed the people of Marikana, particularly the families, the workers, and those that died," he said.
The commission, chaired by retired judge Ian Farlam, is investigating the deaths of 44 people during strike-related violence at Lonmin's platinum mining operations at Marikana, near Rustenburg in the North West, in August 2012.
Thirty-four people, mostly striking mineworkers, were shot dead in a clash with police, over 70 were wounded, and over 250 arrested on August 16, 2012. Police were apparently trying to disarm and disperse them.
In the preceding week, 10 people, including two policemen and two Lonmin security guards, were killed.
Mpofu said Ramaphosa's responsibilities at Marikana went beyond fiduciary duties as a non-executive director of Lonmin.
"Of the parties you say should share the responsibility, you were associated with [the] Lonmin board and management, you were a shareholder, the SA Police Service, the government," said Mpofu.
Ramaphosa said he was not in government (at the time).
Mpofu retorted: "You were not in government but you were exchanging telephone calls with people in government.
"You were a senior member of the ANC [African National Congress]".
Mpofu suggested Ramaphosa was criminally liable for the Marikana events.