Pope Benedict XVI pledged allegiance to his successor before stepping down as leader of the world's 1.2 billion Catholics.
Benedict boarded a white helicopter emblazoned with the Vatican flag for the papal summer residence of Castel Gandolfo near Rome, flying over the Vatican for the last time as Pope.
He arrived at his temporary residence about 15 minutes later and appeared at a window overlooking the public square in Castel Gandolfo, AFP reports.
"I will no longer be pope but a simple pilgrim who is starting out on the last part of his pilgrimage on this Earth," he told thousands of cheering supporters.
"I am happy to be with you surrounded by the beauty of creation. Thank you for your friendship and affection," said the frail but smiling 85-year-old, dressed in his white papal cassock.
At 8pm Benedict's resignation became official and his deputy, Cardinal Tarcisio Bertone, was formally in charge.
Swiss Guards shut the giant wooden doors of the Castel Gandolfo Rome and left their posts after completing their mission to protect the Pope.
Earlier, Benedict bade farewell to cardinals in the Vatican's ornate Clementine Hall.
"Among you there is also the future Pope, to whom I promise my unconditional obedience and reverence," he said.
"Let the Lord reveal the one he has chosen."
As he took leave of his closest aides in an emotional parting ceremony in the Vatican, staff lined the route of his motorcade and applauded.
The bells of St Peter's Basilica rang out as the helicopter took off from the Vatican's helipad.
It was expected that Benedict would remove the personalised signet ring - known as the Fisherman's Ring - before he left office and it will be destroyed, a tradition to ensure the papal seal is not misused.
Workers put seals on the doors of the Vatican papal apartments and the lift leading up to them, to be broken only by the church's next pope.
The German pontiff will continue to be known as Benedict XVI, with the new title of "pope emeritus".
The conclave of 115 cardinals is expected to meet at the Vatican on Monday morning to start planning the election of the next pope.