Francis's visit marked the 200th anniversary of the All Saints' church, furthering a rapprochement between the Vatican and the Anglican Church of England that began last year.
In a further sign of the closer ties, the pope spoke of the “possibility” of a visit to troubled South Sudan with the Archbishop of Canterbury Justin Welby, his Anglican counterpart.
Pope Francis added that such a visit would only be for a single day “because the situation is difficult there”.
South Sudan, which only gained nationhood in 2011, has been engulfed since 2013 by a civil war which has left thousands dead and three million people displaced.
“As Catholics and Anglicans, we are humbly grateful that, after centuries of mutual mistrust, we are now able to recognize that the fruitful grace of Christ is at work also in others,” the pope said in a sermon on Sunday.
“Today we can be encouraged by our gathering.”
Closer ties with other faiths and branches of Christianity have been a priority for Francis since he became pope in 2013.
Last October, he attended a special service in Rome with Welby to mark the 50th anniversary of the first joint prayer of a Catholic pontiff and a head of the Church of England.
The service marked the historic meeting between then archbishop Michael Ramsey and Pope Paul VI.
The Church of England broke away from the Roman Catholic church under British King Henry VIII in the 16th Century, and Anglicans have not recognized the pontiff as their spiritual leader since then.