It's the first time the name is being used by a pope, said CNN Vatican expert John Allen.
Pope Francis chose his name in honor of St. Francis of Assisi because he is a lover of the poor, said Vatican deputy spokesman Thomas Rosica.
"Cardinal Bergoglio had a special place in his heart and his ministry for the poor, for the disenfranchised, for those living on the fringes and facing injustice," Rosica said.
St. Francis, one of the most venerated figures in the Roman Catholic Church, was known for connecting with fellow Christians, Rosica added.
Allen described the name selection as "the most stunning" choice and "precedent shattering."
"There are cornerstone figures in Catholicism," such as St. Francis, Allen said. Figures of such stature as St. Francis of Assisi seem "irrepeatable -- that there can be only one Francis," he added.
The name symbolizes "poverty, humility, simplicity and rebuilding the Catholic Church," Allen said. "The new pope is sending a signal that this will not be business as usual."
In 2010, Pope Benedict XVI recounted how St. Francis was born in 1181 or 1182 as the son of a rich Italian cloth merchant, according to the Vatican website.
After "a carefree adolescence and youth," Francis joined the military and was taken prisoner. He was freed after becoming ill, and when he returned to Assisi, Italy, a spiritual conversion began. He abandoned his worldly lifestyle.
In a famous episode, Christ on the Cross came to life three times in the small Church of St. Damian and told him: "Go, Francis, and repair my Church in ruins," Pope Benedict XVI said, according to the Vatican's website.
"At that moment St. Francis was called to repair the small church, but the ruinous state of the building was a symbol of the dramatic and disquieting situation of the Church herself," Pope Benedict XVI said. "At that time the Church had a superficial faith which did not shape or transform life, a scarcely zealous clergy, and a chilling of love."
Pope Francis succeeds Benedict, who retired.