The Pope has beatified 19th century Cardinal John Henry Newman.
It is the first beatification to be carried out by Benedict since he was elected Pope in 2005, a mark of his lifelong interest in the 19th century clergyman and famous convert to Catholicism.
The Pope said the beatification of Cardinal Newman was an “auspicious” day.
During his four-day visit he has used the Cardinal’s example to highlight the place of the Church in society, the limitations of science, and the need for religion in schools.
He told the crowd: “His insights into the relationship between faith and reason, into the vital place of revealed religion in civilised society, and into the need for a broadly-based and wide-ranging approach to education were not only of profound importance to Victorian England, but continue today to inspire and enlighten many all over the world.
“I would like to pay particular tribute to his vision for education, which has done so much to shape the ethos that is the driving force behind Catholic schools and colleges today.
“Firmly opposed to any reductive or utilitarian approach, he sought to achieve an educational environment in which intellectual training, moral discipline and religious commitment would come together.”
The ceremony brings Newman, who died in 1890, a step closer to becoming the first non-martyred English saint since before the Reformation.
Steady rain failed to dampen the spirits of thousands of the faithful, who trooped into the park armed with folding chairs and dressed in waterproofs.
Sherry Franklin, 50, from Long Ashton, Bristol, a learning support worker, had travelled to the Mass with her sister Irene Cox, 52, a chronic diabetic.
Mrs Franklin said: “To be in the presence of the Pope and so many other Catholics is a dream come true.
“I have a very ill sister and it has been her greatest wish to one day see the Pope in person.
“To be with her and see her dream fulfilled is just so wonderful.”
David Paton, 44, a professor of economics at Nottingham University, was leading a group from the Nottingham parishes of Holy Spirit, St Anne’s and Our Lady’s Cotgrave near Nottingham.
He said: “I think he is obviously a shy and a quiet man but he has got a real way of reaching out to people, not just Catholics.
“People have a right to put their point of view, we have a free country and people can protest, but what I get upset about is when people say things that are not true about the Pope.”
Nina Watson, 52, from Streatham, south London, an Anglican convert, said she had left in the early hours on board a parish coach from the capital.
She said the Pope had been “wonderful and inspiring” during his visit, adding: “He is so clear, and he talks about love and finding God. He has been absolutely wonderful.”
The Pope arrived from London via helicopter before transferring to the Popemobile and on to the service.
Vatican spokesman Federico Lombardi, briefing reporters during the Mass, described the Pope's trip to Britain as “wonderful”.
He said: “Hundreds of thousands of people have met the Pope personally in the street and at the major events and also, through television and the internet, many others have seen him and heard what he has to say.
“I think also that the message that he has about the positive contribution of the Catholic Church and of Christian faith to society has been received very well.”
Commenting on the protests, he said: “If there are critics and protests, this is normal for us and the Pope and it is a positive sign of freedom of expression in this society.”