He was driven into the huge esplanade, sitting in the back of an open-topped vehicle as it passed through the crowds, before descending and starting the service from his position beneath an ancient Egyptian obelisk.
He was admitted to Rome's Gemelli Hospital on Wednesday with breathing difficulties, and later diagnosed with bronchitis.
As the 86-year-old left hospital on Saturday local time, he confirmed he would oversee the Palm Sunday ceremony followed by the Angelus prayer.
He even joked he was "still alive".
"I just felt a malaise, but I wasn't afraid," Italian news agency Ansa quoted him as saying.
After being discharged, the pontiff was seen smiling and waving from his car, before getting out to speak to a crowd.
Instead of heading home, his car drove past the Vatican and stopped at the Basilica of Santa Maria Maggiore. When he came out after praying, people on the street applauded and shouted: "Long live the Pope!"
During another stop, he exited his vehicle to give chocolate Easter eggs to police officers in his motorcade, AP news agency reported.
The pontiff's admission to hospital came ahead of the busiest week in the Christian calendar.
The Holy Week includes a busy schedule of events and services which can be physically demanding.
Vatican spokesman Matteo Bruni said on Friday the Pope was expected to take part in this weekend's service for Palm Sunday.
"I can confirm that, since he is scheduled to leave the hospital tomorrow [Saturday], Pope Francis is expected to be present in St Peter's Square on Sunday for the Eucharistic celebration of Palm Sunday, the Passion of the Lord," Bruni said in a statement.
He will also preside over the hugely popular Easter Mass next Sunday, according to details released by the Vatican.
The Argentine pontiff, who marked 10 years as head of the Catholic Church earlier this month, has suffered a number of health issues throughout his life, including having part of one of his lungs removed at age 21.
He has also used a wheelchair in recent months because of problems related to his knee.
Wednesday's hospitalisation was his second since 2021, when he underwent colon surgery, also at Gemelli.
But the Pope has remained active, visiting the Democratic Republic of Congo and South Sudan in February. The previous month, he led the funeral of his predecessor Pope Benedict XVI.
The pontiff, who has pushed for reforms in the Catholic Church, marked 10 years as its head earlier this month.
Although he has previously said he would consider stepping down if his health failed him, he recently confirmed he had no plans to quit.