Ordained in 1907, Bell was curate of Leeds (Yorkshire) parish church from 1907 to 1910. In 1914 he ceased studies at Christ Church and became chaplain to Archbishop Randall Davidson. He was made dean of Canterbury Cathedral in 1924 and bishop of Chichester in 1929. After Adolf Hitler came to power in Germany, Bell secured asylum in England for Jews and non-Aryan Christians fleeing from the Nazi regime. From 1929 to 1939 he was prominent in movements seeking church reunion, and he developed close relations with the German Confessing Church, which opposed Hitler's regime. During World War II, Bell was an outspoken critic of saturation bombing.

After the war Bell traveled widely on behalf of the ecumenical movement and the World Council of Churches, which he served as chairman and president. He expressed his views in the House of Lords on numerous issues, including his opposition to Britain's decision to make nuclear weapons. Among his works are Randall Davidson (1935), Christian Unity, The Anglican Position (1948), and four volumes of Documents on Christian Unity.