Ramon Guillermo Aveledo, a top opposition leader, said the face-to-face discussions were long overdue.
"Something has gone very wrong for a meeting between the government and the opposition to be rare," he said, adding that they must find a way to stop the bloodshed.
"Violence must be eradicated at the roots," Aveledo said.
Opposition leader Henrique Capriles, who narrowly lost to Maduro in last year's election to replace late socialist leader Hugo Chavez, attended the meeting and was due to speak later.
Eleven opposition delegates and 11 "Chavistas" were given 10 minutes each to speak after Maduro's opening remarks.
Both sides have called on the Roman Catholic Church to be a "good faith" witness. At the start of Thursday's discussions, the Vatican's envoy to Venezuela read a letter from the Pope, encouraging the efforts to find peace.
Maduro, who calls himself the "son" of Chavez and is seeking to preserve popular oil-funded welfare policies while tinkering with his predecessor's statist economic model, said ahead of the talks that he would talk but not negotiate.
Maduro had said before the talks he would be a "traitor" if he began negotiating away the gains of the revolution.
Hardline protesters have openly sought to provoke a "Venezuelan Spring" that would force him from office, but have failed to bring the millions onto the streets they hoped for. The demonstrators have proved persistent, however, with sporadic roadblocks, marches and other protest tactics in some cities.
Maduro says that if the opposition wants to get rid of him, it would have to be via the ballot only. His foes could force a presidential "recall referendum" in 2016 if they garner about 4 million signatures for it. Maduro's six-year term ends in 2019.
Venezuelans across the political spectrum are fed up with violent crime and economic problems including a 57 percent annual inflation rate and shortages of basic products from milk and flour to toilet-paper and car batteries.
Both sides said those issues would figure high in the talks.
Maduro said he had "positive surprises" for the opposition at the discussions, but gave no details. There have been calls for a goodwill release of former security official Ivan Simonovis, who is serving a 30-year sentence for some shootings during a brief coup against Chavez against 2002.