Gallery: Popes John XXIII and John Paul II become saints
The two pontiffs canonised today by Pope Francis are widely seen as representing contrasting faces of the Church.
"These were two men of courage ... and they bore witness before the Church and the world to God's goodness and mercy," Francis said in the ceremony today. "They lived through the tragic events of that (20th) century, but they were not overwhelmed by them,” he added.
John XXIII, who reigned from 1958 to 1963 and called the modernising Second Vatican Council, lived through both world wars.
An Italian often known as the "Good Pope" because of his friendly, open personality, John died before the Second Vatican Council ended its work in 1965 but his initiative set off one of the greatest upheavals in Church teaching in modern times.
The Council ended the use of Latin at Mass, brought in the use of modern music and opened the way for challenges to Vatican authority, which alienated some traditionalists.
In turn, John Paul II, the Pole who reigned for nearly 27 years, witnessed the devastation of his homeland in World War Two and is credited by many with helping end the Cold War and bring down communism.
His pontiff continued many of the reforms but tightened central control, condemned theological renegades and preached a stricter line on social issues such as sexual freedom.
A charismatic, dominant pope, he was criticised by some as a rigid conservative but the adoration he inspired was shown by the huge crowds whose chants of "santo subito!" (make him a saint at once!) at his funeral 2005 were answered with the fastest declaration of sainthood in modern history.