Mr. Novak at a panel discussion with Jeane Kirkpatrick, a U.N. ambassador under President Ronald Reagan. (American Enterprise Institute)

Michael Novak, a Catholic philosopher who helped carve a space for religion in modern politics, diplomacy and economics, arguing that capitalism is the economic system most likely to achieve the spiritual goods of defeating poverty and encouraging human creativity, died Feb. 17 at his home in Washington. He was 83.

The cause was complications from colon cancer, said his daughter Jana Novak.

Mr. Novak, who spent his formative years in the seminary, was widely recognized as one of the most influential Catholic theologians of his generation. He was the 1994 recipient of the Templeton Prize, which honors makers of an “exceptional contribution to affirming life’s spiritual dimension” and is accompanied by a monetary award exceeding that of the Nobel Prize.

In a measure of Mr. Novak’s influence within the Catholic Church, he was received and consulted by Popes John Paul II and Benedict XVI. He was at times a professor, a columnist, chief U.S. delegate to the U.N. Human Rights Commission and, for several decades, a scholar at the American Enterprise Institute, the conservative think tank in Washington.

Mr. Novak was among several scholars who “brought serious religious thought to Washington in a way that it had not been present before,” George Weigel, a distinguished senior fellow at the Washington-based Ethics and Public Policy Center, said in an interview.

He credited Mr. Novak with demonstrating to an “audience of insiders” a “way of thinking that was not merely statistical or ideological but was perhaps more deeply reflective of enduring human questions and problems.”

Mr. Novak wrote a shelf full of books on topics ranging from nuclear weapons to atheism to social justice to sports. But he was best known for his economic writings, particularly the book “The Spirit of Democratic Capitalism” (1982).

“Democratic capitalism,” he wrote, is “neither the Kingdom of God nor without sin. Yet all other known systems of political economy are worse. Such hope as we have for alleviating poverty and for removing oppressive tyranny — perhaps our last, best hope — lies in this much despised system.”

Mr. Novak’s book found resonance around the world. It was illegally distributed in Poland, where the Solidarity movement helped defeat communism. His writings were credited with influencing Václav Havel, the dissident playwright who became the first president of Czechoslovakia after communism, and Prime Minister Margaret Thatcher of Britain.

In affairs across the Atlantic, Mr. Novak was a forceful critic of liberation theology as it was espoused in Latin America, where many adherents argued that the church should provide economic deliverance for the poor through leftist political ideologies.

Critics of Mr. Novak charged that he overlooked the severe inequalities often wrought by capitalism: “Michael Novak preaches capitalism’s virtues to Christians,” Arthur Jones, a columnist for the National Catholic Reporter, once wrote. “The breakthrough will come when he simultaneously preaches Christian virtues to his capitalist backers.”

Mr. Novak acknowledged that “Judaism and Christianity do not require democratic capitalism.” But, he continued, “it is only that without it they would be poorer and less free.”

In the sphere of international affairs, Mr. Novak tussled with church leaders over Catholic teaching on “just war.” He regarded the nuclear deterrent as a moral means of prevailing over the Soviet Union in the Cold War and defeating what Weigel said they and like-minded thinkers considered Communism’s “defective” and “downgraded view of the human person.”

It was under President Ronald Reagan that Mr. Novak served on the U.N.’s human rights body. Communism, Weigel said, explaining his and Mr. Novak’s position, “denied that the human person was made in the image and likeness of God, and it’s that image in us that is the root, we would argue, of the human dignity from which spring human rights.”

In the cultural arena, Mr. Novak wrote frankly of “radical feminism, gay liberation, utopian socialism and geopolitical neutralism” and “the cheaply radical young graduates of . . . Catholic universities.” But he also drew praise for the openness with which he approached religious dialogue, such as in his book “No One Sees God: The Dark Night of Atheists and Believers” (2008).

“The line of belief and unbelief,” he wrote, “is not drawn between one person and another, normally, but rather down the inner souls of all of us.”

Michael John Novak Jr. was born to a Slovak American family in Johnstown, Pa., on Sept. 9, 1933. His father was an insurance salesman, and his mother was a homemaker. A brother, Richard Novak, became a priest and was killed amid political upheaval in Bangladesh in 1964.

Mr. Novak joined the Congregation of Holy Cross at 14 and studied for the priesthood but ultimately left the order.

“It was not untypical of bright idealistic Catholic boys to want to enter the priesthood, though your immediate circle of friends thought you were faintly crazy,” Mr. Novak told the New York Times in 1982. He said that he aspired to be a novelist, but “didn’t see how I could do the independent thinking and traveling I wanted to do, and do it in community and under obedience.”

His first book, a novel titled “The Tiber Was Silver” (1961), centered on an American seminarian who ventures to Rome and wrestles with the question of whether he can pursue his religious vocation as well as his love of painting.

Mr. Novak received a bachelor’s degree in philosophy from Stonehill College in Easton, Mass., in 1956, a bachelor of sacred theology degree from the Pontifical Gregorian University in Rome in 1958 and a master’s degree in the history and philosophy of religion from Harvard University in 1966.

He positioned himself initially on what he described as the “anticapitalist left.” In the early years of his career, he taught at schools including Stanford University, the State University of New York and Syracuse University and did political work for Democrats including Sen. George S. McGovern (S.D.), a torchbearer for liberalism despite his landslide loss to President Richard M. Nixon (R) in 1972.

Mr. Novak supported the liberalization of the Catholic Church brought about by the Second Vatican Council in the 1960s — a position he later recanted — and opposed such church teachings as its prohibition on contraception. His early liberal writings included the book “The Open Church” (1964), about the effects of Vatican II, and “A Theology for Radical Politics” (1969).

Over the next several years, Mr. Novak shifted rightward, economically and culturally — an evolution detailed in the memoir “Writing From Left to Right: My Journey From Liberal to Conservative” (2013).

Contributing to his growing disillusionment with the left was the unsympathetic reception of his book “The Rise of the Unmeltable Ethnics” (1972). In that volume, he railed against what he regarded as the marginalization of working-class Eastern European and other ethnic groups by the elite, largely Protestant establishment.

In 1978, Mr. Novak joined AEI, where he retired in 2010. He served at the time of his death on the faculty of Catholic University.

Mr. Novak’s wife of 46 years, the former Karen Laub, died in 2009. Survivors include three children, Richard L. Novak of San Antonio, Tanya Holton of Boston and Jana Novak of Oklahoma City; a sister, Mary Ann Novak of Washington; a brother, Benjamin Novak of Ave Maria, Fla.; and four grandchildren.

With his daughter Jana, Mr. Novak wrote “Tell Me Why: A Father Answers His Daughter’s Questions About God” (1998). In that volume, he articulated his idea of what God is — and is not.

“He is not ‘the Big Guy upstairs,’ nor the loud booming voice that Hollywood films affect for God. . . . There are hosts of bogus pictures for God: the Watchmaker beyond the skies, the puppeteer of history,” he wrote. “If you wish to find him, watch for him in quiet and humility — perhaps among the poor and broken things of earth.

“There are people,” he continued, “who looked into the eyes of the most abandoned of the poor and saw infinite treasure there, treasure without price, and there found God dwelling.”