With the fall of France to Nazi Germany he was returned to civilian life and began doctoral studies, completing in 1942 his thesis on the spiritual doctrine of Gregory of Nyssa.

Beginning in the 1950s he produced several historical studies which included The Bible and the Liturgy, The Lord of History, and From Shadows to Reality that furnished background for the development of Covenantal Theology.

[2] Thoroughly grounded in the Fathers of the Church, who worked from Scripture, Daniélou generally avoided the neo-Thomistic terminology and approach and used a more relational vocabulary, emphasizing our self-gift in response to God's gift in Jesus Christ, with the gradual unveiling of the Trinitarian life in history.

As a result, he was ordained to the episcopal titular see of Taormina, and assigned the title of Cardinal-Deacon of San Saba, a Jesuit-run parish in Rome.

[5] Rather like his theology professor Henri de Lubac, Daniélou twice refused the cardinalate but eventually accepted at the insistence of Paul VI.