Five other lesser-known individuals were declared also saints during a mass that was attended by tens of thousands of people, church-run Vatican News reported.
"All these saints, in different contexts, put today's word into practice in their lives, without lukewarmness, without calculation, with the passion to risk everything and to leave it all behind," Francis said at the conclusion of his homily. "Brothers and sisters, may the Lord help us to imitate their example."
Francis signed decrees in March to make Romero and Pope Paul VI eligible for sainthood. Romero, an archbishop in El Salvador, was killed by a sniper moments after he finished giving a sermon in 1980. Romero spoke out against poverty and his government's role in violence in the nation.
"It is wonderful that together with him and the other new saints today, there is Archbishop Romero, who left the security of the world, even his own safety, in order to give his life according to the Gospel, close to the poor and to his people, with a heart drawn to Jesus and his brothers and sisters," Francis said Sunday.
Paul VI was pope from 1963 to 1978. His tenure included reforms such as allowing mass to be celebrated in languages other than Latin. He also doubled down on the church's opposition to birth control.
"Even in the midst of tiredness and misunderstanding, Paul VI bore witness in a passionate way to the beauty and the joy of following Christ totally," Francis said Sunday.