He led a major $10 million campaign to raise funds for additional construction on the Cathedral of St. John the Divine, and directed a program to train and employ men from the neighborhood as skilled artisans during the Great Depression and later.

In 1939-40, Manning took a leadership role in the successful effort to force the City University of New York to rescind their offer of a professorship to the philosopher Bertrand Russell.

"[citation needed] One year prior to the U.S. entering World War I, Manning said: Our Lord Jesus Christ does not stand for peace at any price...Every true American would rather see this land face war than see her flag lowered in dishonor...I wish to say that, not only from the standpoint of a citizen, but from the standpoint of a minister of religion...I believe there is nothing that would be of such great practical benefit to us as universal military training for the men of our land.

[7] In 1933, he attended a rally at Madison Square Garden alongside Reform Jewish Rabbi Stephen Wise, protesting anti-Jewish legislation by the Nazi regime in Germany.

[9] In 1939–40, Bishop Manning took a leadership role in the successful effort to force the City University of New York to rescind their offer of a professorship to the philosopher Bertrand Russell.

[10] On his retirement, Time magazine noted that "his vigilant guardianship of orthodoxy has often made New York’s Bishop look something of a prim curmudgeon" as well as "his battles with advocates of easy divorce, isolationists, opponents of pan-Christian unity, proponents of a Presbyterian-Episcopalian merger.

"[11] The New York Times, fifteen years after his death, called him "one of this country's best-known churchmen" and wrote that his forthright and fiery sermons, based on the belief that religion is involved in all of life, raised scores of controversies.