Pope Leo was cheered by thousands of worshippers in St Peter's Square as he led a prayer service after undergoing lung cancer surgery.
The pontiff appeared at the window of his Apostolic Palace to choruses of 'Viva il papa! (Hooray for the Pope!)' before rounding off a tough week by delivering his first Angelus prayer since leaving hospital.
The 71-year-old leader of the world's 1.4 billion Catholics thanked the masses of well-wishers, adding he will resume work 'gradually'.
It was a triumphant moment for the Pope having been released from hospital on Saturday, just four days after surgery to remove a cancerous mass from his lung.
He went in for the 90-minute procedure on Tuesday morning after a lesion was found on his chest and he was later diagnosed with adenocarcinoma, the most common type of lung cancer, having had part of his right lung removed.
Histological testing of the tumour and related lymph nodes is underway. The results, along with details of the tumour's molecular and genetic makeup, will help doctors determine whether the Pope needs additional treatment.
Options include chemotherapy, a combination of chemotherapy and immunotherapy, or targeted oral therapy based on the tumour's genetic characteristics.
Smiling from a window of the Vatican's Apostolic Palace as he spoke to pilgrims below in a firm, clear voice on Sunday, the first US Pope thanked people across the world for their prayers and said he would now begin to resume his normal schedule.
Pope Leo was cheered by thousands of worshippers in St Peter's Square on Sunday as he led a prayer service after undergoing lung cancer surgery
The 71-year-old leader of the world's 1.4 billion Catholics thanked the masses of well-wishers, adding he will resume work 'gradually'
The pontiff appeared at the window of his Apostolic Palace to choruses of 'Viva il papa! (Hooray for the Pope!)'
He told the faithful that he had 'truly felt your support,' and expressed 'particular gratitude to the doctors, nurses and all the staff at Gemelli hospital' where he was treated
'Having overcome this delicate phase... I will now gradually resume my activities, always with the help of God and your prayers,' Leo - who made his way to the service unaided - said.
He also urged pilgrims waiting below under cloudy skies to set aside any selfish ambitions and serve God 'without compromise'.
The pontiff said the experience of the last week 'has made me feel especially close to those facing illness and infirmity'.
He told the faithful that he had 'truly felt your support', and expressed 'particular gratitude to the doctors, nurses and all the staff at Gemelli hospital' where he was treated.
The Pope paused for a moment and waved to the crowd before retreating into his apartment in the Apostolic Palace.
A delegation from Africa in Rome for a congress danced and ululated after the Pope's blessing.
Ahead of a remarkable comeback on Sunday, Leo told a reporter he was doing 'much better' as he drove away from Rome's Gemelli hospital to return to the Vatican, well ahead of the week-long hospital stay initially anticipated.
Leo's next major engagement is an ambitious trip to Uruguay, Argentina and Peru from November 6-17, including a dozen flights and two helicopter rides to high altitudes.
His surgeon, Dr Stefano Margaritora, told Vatican News on Saturday there are 'no clinical reasons' to preclude the trip.
'The Holy Father has put his heart and soul into his recovery,' he said, adding that he expected the Popeto recover fully from surgery 'in another 10 days or so'.
'As for a long trip involving air travel in about three weeks, I would say there are no clinical reasons why it should not take place,' Dr Margaritora added.
The Pope has offered a rare level of transparency after announcing last Sunday to the faithful gathered in St Peter's Square that doctors had identified a nodule on his lung, and that it would be removed.
Pope Leo revealed his diagnosis to millions around the world on live television almost as an aside at the end of his blessing.
The Vatican has previously been extremely secretive about the health of Popes – a practice encapsulated in the Italian saying, 'The Pope is fine until he's dead.'
Pope Leo XIV smiled and waved to well-wishers on Saturday as he was released from hospital, four days after undergoing surgery to remove a cancerous mass from his lung
His personal physician and surgeon said in an earlier statement that Pope Leo was 'deemed fit for discharge from the hospital'
Pope Leo XIV was pictured on Friday celebrating Mass at the Agostino Gemelli Polyclinic, Rome
Since his surgery, Pope Leo has given strong indications he has been recovering well, including by holding a phone call with Russian president Vladimir Putin, meeting with top aides and celebrating Mass in a hospital chapel.
His personal doctor has also indicated a good post-operative recovery that has allowed the pontiff to carry on 'normal daily activities completely on his own'.
On Saturday, the Vatican released the first images of Leo since his lung cancer surgery, showing him standing at an altar in a hospital chapel.
The Pope presided alone over the liturgy, distributing Communion to medical personnel and Vatican gendarmes, spokesman Matteo Bruni said.