The Archbishop of Canterbury has paid tribute to former Pope Benedict XVI as "one of the greatest theologians of his age" following his death at the age of 95.

Archbishop Justin Welby said the Pope Emeritus had been "stalwart" in his defence of the Church and called his decision to resign in 2013 "courageous and humble". 

"Today I join with the church throughout the world, and especially with the Holy Father, Pope Francis, and all in the Catholic Church, in mourning the death of Pope Emeritus Benedict XVI," the Archbishop said in a statement. 

"In Pope Benedict's long life and ministry of service to Christ in His Church he saw many profound changes in the church and in the world.

"He lived through the Nazi regime in Germany and served briefly in the Second World War.

"As a younger theologian and priest he witnessed first-hand the discussions of the Second Vatican Council.

"As a professor and then as an Archbishop he lived in a divided Germany but saw too the fall of the Berlin Wall and the reunification of his homeland." 

Benedict served as pope from 2005 to 2013, when he retired at the age of 85 citing his "advanced age". At the time, he said his decision to step down was "for the good of the Church".

Archbishop Welby paid tribute to the former pope's commitment to the Church and his faithfulness to Christ in his preaching, writing and prayer. 

"Pope Benedict was one of the greatest theologians of his age – committed to the faith of the Church and stalwart in its defence," said Welby.

"In all things, not least in his writing and his preaching, he looked to Jesus Christ, the image of the invisible God. It was abundantly clear that Christ was the root of his thought and the basis of his prayer.

"In 2013 Pope Benedict took the courageous and humble step to resign the papacy, the first Pope to do so since the fifteenth century.

"In making this choice freely he acknowledged the human frailty that affects us all. In his retirement in Rome he has led a life of prayer and now he has gone to the eternal rest granted by the Father.

"In his life and ministry Pope Benedict strove to direct people to Christ. May he now rest in Christ's peace, and rise in glory with all the Saints."