The newly appointed Archbishop Fridolin Ambongo called on President Joseph Kabila's government to hold the elections on Dec. 30, as announced last week.
Cheers greeted his homily at the Notre Dame Cathedral of Kinshasa.
"The real peace excludes egoism, regionalism, tribalism, division and categorization that pushed us apart," said Ambongo. "In this critical period in the history of our country, I invite each of you to have a sense of responsibility, and to embrace nonviolence, so we may make it through December 30th 2018 that elections happen in peace and truth."
Congo's Catholic church has a been a longtime supporter of democracy in the country and has urged Kabila to hold elections, which have been postponed for two years.
The church has been a key player in negotiations after Kabila refused to step down at the end of his mandate in 2016.
"Real peace, today in our country, the peace that comes from Jesus Christ, that peace requires that the elections are held on schedule, on the 30th of December 2018," said Ambongo.
"Real peace ... is a peace that also calls for the results when they are announced to reflect the real will of the people," he said.