It was a decidedly different style of papacy than his tradition-minded predecessor who tended to stay ensconced in the frescoed halls of the Vatican.
The break from Benedict XVI's pontificate was evident even in Francis' wardrobe choices: He kept the simple iron pectoral cross of his days as bishop and eschewed the red cape that Benedict wore when he was presented to the world for the first time in 2005 - choosing instead the simple white cassock of the papacy.
And in his first Mass as pope, Francis showed how different he would be as a pastor, giving an off-the-cuff homily about the need to walk with God, build up his church and confess - at one point referring to children building sand castles on the beach.
It was a far simpler message than the dense, three-page discourse Benedict delivered in Latin during his first Mass as pope in 2005.
The difference in style was a sign of Francis' belief that the Catholic Church needs to be at one with the people it serves and not impose its message on a society that often doesn't want to hear it, Francis' authorised biographer, Sergio Rubin, said.
"It seems to me for now what is certain is it's a great change of style, which for us isn't a small thing," Mr Rubin said, recalling how the former Cardinal Jorge Bergoglio would celebrate Masses with homeless people and prostitutes in Buenos Aires.
"He believes the church has to go to the streets," he said, "to express this closeness of the church and this accompaniment with those who are suffering."
Francis began his first day as pope making an early morning visit in a simple Vatican car to a Roman basilica dedicated to the Virgin Mary and prayed before an icon of the Madonna.
He had told a crowd of some 100,000 people packed in rain-soaked St. Peter's Square just after his election that he intended to pray to the Madonna "that she may watch over all of Rome."
He also told cardinals he would call on retired Pope Benedict XVI, but the Vatican said the visit wouldn't take place for a few days.
The main item on Francis' agenda was his inaugural afternoon Mass in the Sistine Chapel, where cardinals elected him leader of the 1.2 billion-strong church in an unusually quick conclave.
At the start of the Mass, Francis exchanged words with Monsignor Guido Marini, the Vatican's master of liturgical ceremonies who under Benedict ushered in a far more traditional style of liturgy, heavy on Gregorian chant, Latin and the silk-brocaded vestments of the pre-Vatican II church.
Vatican officials confirmed reports that Msgr Marini was somewhat put off by Francis' refusal last night to wear the formal papal red cape when he emerged on the loggia overlooking St Peter's Square to be introduced to the crowd. Benedict was known to favour many of the trappings of the papacy, including the elaborate vestments and ceremonial gear used by popes past.
Traditionalists had rejoiced with Benedict's return to these elements of the pre-Vatican II church, arguing it was the true church and not the one spoiled by the council's reforms.
Francis, the first Jesuit pope and first non-European since the Middle Ages, decided to call himself Francis after St. Francis of Assisi, the humble friar who dedicated his life to helping the poor.
The new pope, known for his work with the poor in Buenos Aires' slums, immediately charmed the crowd in St. Peter's, which roared when his name was announced and roared again when he emerged on the loggia of the basilica with a simple and familiar: "Brothers and sisters, good evening."
By this morning, members of his flock were similarly charmed when Francis stopped by the Vatican-owned residence where he routinely stays during visits to Rome and where he stayed before the start of the conclave.
"He wanted to come here because he wanted to thank the personnel, people who work in this house," said The Rev Pawel Rytel-Andrianek, who is staying at the residence. "He greeted them one by one, no rush, the whole staff, one by one."
He then paid the bill.
"People say that he never in these 20 years asked for a (Vatican) car," he said. "Even when he went for the conclave with a priest from his diocese, he just walked out to the main road, he picked up a taxi and went to the conclave. So very simple for a future pope."
Francis displayed that same sense of simplicity and humility immediately after his election, shunning the special sedan that was to transport him to the hotel so he could ride on the bus with other cardinals, and refusing even an elevated platform from which he would greet them, according to US Cardinal Timothy Dolan.
"He met with us on our own level," Cardinal Dolan said.
The 76-year-old Bergoglio, said to have finished second when Pope Benedict XVI was elected in 2005, was chosen on just the fifth ballot to replace the first pontiff to resign in 600 years.
Francis urged the crowd to pray for Benedict and immediately after his election spoke by phone with the retired pope, who has been living at the papal retreat in Castel Gandolfo south of Rome. A visit to Benedict would be significant because Benedict's resignation has raised concerns about potential power conflicts emerging from the peculiar situation of having a reigning pope and a retired one.
Benedict's long-time aide, Monsignor Georg Gaenswein, accompanied Francis to the visit at St. Mary Major. In addition to being Benedict's secretary, Msgr Gaenswein is also the prefect of the papal household and will be arranging the new pope's schedule.
The new pontiff brings a common touch. The son of middle-class Italian immigrants, he denied himself the luxuries that previous cardinals in Buenos Aires enjoyed. He lived in a simple apartment, often rode the bus to work, cooked his own meals and regularly visited slums that ring Argentina's capital.
Francis considers social outreach, rather than doctrinal battles, to be the essential business of the church.
As the 266th pope, Francis inherits a Catholic church in turmoil, beset by the clerical sex abuse scandal, internal divisions and dwindling numbers in parts of the world where Christianity had been strong for centuries.
