The Prime Minister visited the charity's head office in Witney, Oxfordshire, which is his parliamentary constituency.
He said: "It has been a pleasure to visit Open Doors in Witney today to mark 60 years since they began helping persecuted Christians.
"Now working in over 65 countries, Open Doors does fantastic work: providing invaluable support to those in crisis, as well as bringing together those of different backgrounds and religions to help and support one another.
"It has been humbling to hear the stories of the great courage shown by Christians facing persecution and the wonderful examples of how communities can work together, with the church leading the way.
"Standing up for religious freedom is a priority for my Government. We are committed to promoting and protecting the right to freedom of religion or belief as one of the foundations of human rights.
"No matter what faith we follow, charity, compassion, responsibility and forgiveness are values which speak to us all."
Mr Cameron was also given a handwritten New Testament written by a woman in Egypt during two years of literacy classes, which was funded by Open Doors.
Open Doors supports persecuted Christians by providing food, medicine, counselling, legal aid, safe houses and schools.
It also provides Christian literature and compiles an annual list of countries where believers are the most persecuted called the World Watch List.
North Korea has been at the top of this list for some time, and its estimated up to 70,000 Christians are in prison there because of their faith.
The 2016 list will be launched at Parliament on January 16th.
Open Doors Chief Executive Lisa Pearce said: "In the midst of the current global turmoil, Open Doors is working to support people who suffer for their Christian faith.
"We continue to work towards the day when everybody throughout the world will be free to follow the religion of their choice without the fear of persecution."
