Thousands have witnessed the Pope's beatification of 19th Century churchman Cardinal John Henry Newman, before the pontiff's departure by air for Rome.
Pope Benedict told more than 50,000 people at a Mass in Birmingham's Cofton Park that they were celebrating the cardinal's "outstanding holiness".
Prime Minister David Cameron told the Pope shortly before he left that Britain "cherished faith".
The Pope replied the diversity of Britain was an "enriching challenge".
He had earlier urged bishops meeting at St Mary's College, Oscott, to "make reparation" for child abuse by priests.
The Pope flew out of Birmingham airport at the end of his four-day UK tour.
He was praised in a speech at the airport by David Cameron, who said the Pope had "offered a message to each and every one of us".
The prime minister, whose father recently died, continued: "When you think of our country, think of it as one that not only cherishes faith, but one that is deeply, but quietly, compassionate.
"I see it in the incredible response to the floods in Pakistan.
"And in my own life, I have seen it in the many, many kind messages that I have had as I have cradled a new daughter and said goodbye to a wonderful father."
The leader of Roman Catholics in England and Wales, the Most Reverend Vincent Nichols, said the Pope's visit had been "better than he expected".
He said people had been able to see Pope Benedict as he really was - "gentle, sensitive and eloquent".
Archbishop Nichols said the Pope had been deeply encouraged and moved by his reception, and he would see the country in a new light.
On leaving, the Pope used his speech to pay tribute to Britain's multicultralism.
He said: "I have been able to meet representatives of the many communities and cultures of British society.
"The diversity of modern Britain is a challenge.
"But it also represents a great opportunity for the enrichment of the entire community."
He made the comments after the start of his state visit was marred when one of his aides, Cardinal Walter Kasper, reportedly said arriving at Heathrow airport was like landing in a "Third World" country.
Earlier in the day crowds cheered in Birmingham after the beatification, was carried out. The Pope paid tribute to Cardinal Newman's insights into the vital place of "religion in civilised society".
In his homily, he also marked the 70th anniversary of the Battle of Britain by paying tribute to those who sacrificed their lives resisting the "evil ideology" of the Nazi regime.
The German-born Pope, who was forced to join the Hitler Youth as a 14-year-old schoolboy, told worshippers: "For me as one who lived and suffered through the dark days of the Nazi regime in Germany, it is deeply moving to be here with you on this occasion, and to recall how many of your fellow citizens sacrificed their lives, courageously resisting the forces of that evil ideology."
And, paying tribute to Cardinal Newman, the pontiff said the beatification was an "auspicious" day.
"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," he said.
Rain fell steadily on the thousands of pilgrims at Cofton Park who gathered for the open Mass.
Anglican convert Nina Watson, 52, from Streatham, south London said she had left home in the early hours to embark on a coach trip to Birmingham.
She said the Pope had been "wonderful and inspiring" during his UK visit.
"He is so clear, and he talks about love and finding God. He has been absolutely wonderful," she said.
Frances McHugh, 67, a retired secretary from Shirley, Birmingham, and a parishioner at Our Lady of the Wayside Church described the pontiff as "a very holy man", adding that "it is lovely to see him in this country".
"We have not had to go to see him in Rome, he has come to see us," she said.
During the trip, Pope Benedict XVI has spoken out about what he called the "marginalisation" of Christianity and the march of "aggressive secularism".
Thousands marched in London on Saturday to protest against the Pope's visit.
Campaign group Protest the Pope estimated around 20,000 people took part; however, police were unable to confirm this figure.
Speaking in Birmingham, Mr Cameron told the Pope: "Faith is part of the fabric of our country.
"It always has been and it always will be."
In his speech at the airport, Mr Cameron said people did not have to share a faith to see the value of the "searching questions" that the Pope had posed about "society and how we treat ourselves and each other".
"You have really challenged the whole country to sit up and think, and that can only be a good thing," he said.
"Because I believe we can all share in your message of working for the common good... and that we all have a social obligation to each other, to our families and our communities."