Thousands of people arrived at Rizal Park on today morning, hours before the Mass is due to begin.
The Vatican said Pope Francis would dedicate the service in part to the victims of Typhoon Haiyan, which devastated the country in 2013.
The Mass will be the Pope's final full day in the Philippines, where there are 80 million Catholics, concluding his six-day tour of Asia.
Philippine officials have estimated that as many as six million people may attend the Mass on Sunday afternoon, according to local media.
Some people camped outside the park overnight to be the first ones admitted when the gates opened early on Sunday morning.
Before the final mass, the Pope held morning meetings with religious leaders and young people at the University of Santo Tomas which is the biggest Catholic university in Asia.
Pope Francis opened his meeting with over 20,000 students by remembering the 27-year-old woman who had died during his visit to Tacloban.
Earlier, police had reported that she had been killed when scaffolding collapsed after Saturday's Mass.
The Pope then listened to several children speak about their experiences of growing up on the streets.