During the service the Pope told the congregation that “God wants the unity of his people,” according to Catholic News Service.
He went on to tell Catholic and Anglican bishops to “work as instruments of communion always and everywhere.”
The church of St Gregory is named after the sixth century pope who dispatched missionaries to England to spread Christianity.
The celebration comes days after Francis returned from Georgia, where he worked to improve relations with the Georgian Orthodox Church.
Francis will shortly travel to Sweden to mark the 500th anniversary of the Protestant Reformation.