[1] As representative of the United States Conference of Catholic Bishops and consultant to the religious affairs section of the Allied High Commission, he helped draft and promote the 1943 Declaration on World Peace, an interfaith statement of principles for postwar reconstruction.

[2] Similarly, Murray advocated religious freedom and pluralism as defined and protected by the First Amendment of the US Constitution, which contradicted Catholic doctrines of church-and-state relations before Vatican II.

His best-known book, We Hold These Truths: Catholic Reflections on the American Proposition (1960), collects a number of his essays on such topics.

The project was both nationally influential and personally formative, as it deepened Murray's understanding of and esteem for American constitutional law.

[citation needed] In his increasingly public role, several American bishops consulted Murray on legal issues such as censorship and birth control.

[7] After his death in 1967, his obituary in Time declared that he had been responsible for incorporating /the US secular doctrines of church-state separation and freedom of conscience in to the spiritual tradition of Roman Catholicism" despite the efforts of the "ultra conservative" faction in the Church.

[1] Murray’s claim that a "new moral truth" had emerged outside the Church led to conflict with Cardinal Alfredo Ottaviani, Pro-Secretary of the Vatican Holy Office.

[10] He continued to write on the issue by claiming that the arguments offered by the final decree were inadequate even if the affirmation of religious freedom was unequivocal.

In 1966, prompted by the Vietnam War, he was appointed to serve on Lyndon Johnson's presidential commission, which reviewed Selective Service classifications.

He suggested greater reforms, including a restructuring of the Church, which he saw as having overdeveloped its notion of authority and hierarchy at the expense of the bonds of love that had from the start defined the authentically Christian life.