Red-hatted cardinals, priests, candle-carrying friars and helmeted Swiss Guards walked slowly into the vast, sunlit esplanade as a male choir chanted psalms and prayers in Latin while the great bells of the basilica tolled.
The body of the 88-year-old pope, who died two days ago in his rooms at the Santa Marta guesthouse after suffering a stroke, was held aloft on a wooden platform by 14 white-gloved, black-suited pallbearers.
"Dear brothers and sisters, with deep sorrow we now accompany the mortal remains of our Pope Francis to the Vatican Basilica," said the Irish-American cardinal Kevin Farrell at the start of the ceremony.
As the coffin crossed St Peter's Square, a crowd of several thousand broke into repeated applause - a traditional Italian sign of respect at such events.
Pope Francis, who spent five weeks in hospital earlier this year being treated for double pneumonia, last appeared in public on Sunday, when he surprised pilgrims by being driven around the packed square in his white, open-topped popemobile.
His body will lie in state in St Peter's Basilica until Friday evening, allowing faithful to pay their respects.
"He's like a member of the family. Somebody very close to our hearts, somebody who made the church very accessible to everybody and inclusive to everybody," said Rachel Mckay, a pilgrim from Britain who was in the square.
His funeral is set for Saturday and will draw heads of state and government from around the world, including US President Donald Trump, who clasherepeatedly with the pope on social issues.
Leaders from Italy, France, Germany, Britain, Ukraine, EU institutions and Francis' home nation of Argentina have also confirmed their presence.
At least 200,000 people are expected to attend the outdoor service, the head of Italy's civil protection agency, Fabio Ciciliano, told the Corriere della Sera newspaper.
A conclave to choose the new pope is not expected to start before May 6, with cardinals now flocking to Rome only due to decide the date following what are often prolonged discussions.
There is no clear frontrunner to succeed Francis, although British bookmakers have singled out Luis Antonio Tagle, a reformer from the Philippines, and Pietro Parolin, from Italy, as early favourites.
In the meantime, in the period known as the "sede vacante" (vacant seat) for the global Catholic Church, cardinal Farrell is in charge of day-to-day affairs.
