In the moments before he was to face a vote on becoming speaker of the House this week, Representative Mike Johnson posted a photograph on social media of the inscription carved into marble atop the chamber’s rostrum: “In God We Trust.”

His colleagues celebrated his candidacy by circulating an image of him on bended knee praying for divine guidance with other lawmakers on the House floor.

And in his first speech from the chamber as speaker, Mr. Johnson cast his ascendance to the position second in line to the presidency in religious terms, saying, “I believe God has ordained and allowed each one of us to be brought here for this specific moment.”

Mr. Johnson, a mild-mannered conservative Republican from Louisiana whose elevation to the speakership on Wednesday followed weeks of chaos, is known for placing his evangelical Christianity at the center of his political life and policy positions. Now, as the most powerful Republican in Washington, he is in a position to inject it squarely into the national political discourse, where he has argued for years that it belongs.

Mr. Johnson, 51, the son of a firefighter and the first in his family to attend college, has deep roots in the Southern Baptist Convention, the nation’s largest Protestant denomination. For years, Mr. Johnson and his wife, Kelly, a licensed pastoral counselor, belonged to First Bossier, whose pastor, Brad Jurkovich, is the spokesman for the Conservative Baptist Network, an organization working to move the denomination to the right.

Mr. Johnson also played a leading role in efforts to overturn the results of the 2020 presidential election and has expressed skepticism about some definitions of the separation of church and state, placing himself in a newer cohort of conservative Christianity that aligns more closely with former President Donald J. Trump and that some describe as Christian nationalism.

“Speaker Johnson really does provide a near-perfect example of all the different elements of Christian nationalism,” said Andrew Whitehead, a sociologist at Indiana University-Purdue University Indianapolis. He said those included insisting on traditionalist family structures, “being comfortable with authoritarian social control and doing away with democratic values.”

Mr. Johnson declined an interview request and did not respond to a request for comment about whether he considers himself a Christian nationalist. But the little-known speaker of the House has made clear that his faith is the most important thing to know about him, and in previous interviews, he has said he believes “the founders wanted to protect the church from an encroaching state, not the other way around.”

Over the arc of his career, Mr. Johnson, a lawyer and a member of the Louisiana Legislature before his election to Congress, has been driven by a belief that Christianity is under attack and that Christian faith needs to be elevated in the public discourse, according to a review of his appearances on talk shows and podcasts, as well as legislative speeches and writings over the past two decades.

He refers to the Declaration of Independence as a “creed” and describes it as a “religious statement of faith.” He believes that his generation has been wrongly convinced that a separation of church and state was outlined in the Constitution.

In his first interview as speaker, Mr. Johnson described himself to the Fox News host Sean Hannity as “a Bible-believing Christian” and said that to understand his politics, one only need “pick up a Bible off your shelf and read it. That’s my worldview.”

That includes opposition not just to abortion, which he has called “a holocaust,” and same-sex marriage, but to homosexuality itself, which he has written is “inherently unnatural” and a “dangerous lifestyle.” He is the sponsor of a bill that would prohibit the use of federal funds for providing education to children under 10 that included L.G.B.T.Q. topics — a proposal that critics called a national version of Florida’s “Don’t Say Gay” law.

In a 2006 column for Townhall, a conservative website, Mr. Johnson railed against “the earnest advocates of atheism and sexual perversion.”

“This sprawling alliance of anti-God enthusiasts has proven frighteningly efficient at remaking America in their own brutal, dehumanizing image,” he wrote.

He added: “In the space of a few decades, they have managed to entrench abortion and homosexual behavior, objectify children into sexual objects, criminalize Christianity in the popular culture, and promote guilt and self-doubt as the foremost qualities of our national character.”

In Washington, the prime role of religion in Mr. Johnson’s political life is often the first thing colleagues learn about when they meet him.

“It doesn’t take long,” said Representative Byron Donalds, Republican of Florida, who said that Mr. Johnson often begins meetings by leading a prayer. “You’ll pretty much know that in the first five minutes. He’s truly a humble man.”

Yet he is not shy about framing his political career as a divinely driven battle to put religion at the center of American policy and lawmaking. From gun violence to abortion to immigration, Mr. Johnson’s policy views are shaped by his belief that too many Americans are “denying existence of God himself.”

In remarks to a Louisiana congregation in 2016, Mr. Johnson linked school shootings to no-fault divorce laws (he is in a covenant marriage with his wife, which makes divorce more difficult), “radical feminism” and legal abortion. “We’ve taught a whole generation — couple of generations, now — of Americans that there is no right and wrong,” he said then.

In an episode of his podcast, “Truth Be Told,” Mr. Johnson explained how his religion drives his hard-line immigration stance, arguing that while the Bible teaches Christians to practice “personal charity,” that commandment was “never directed to the government.”

“The left is taking it and using it out of context,” Mr. Johnson said. Welcoming the stranger, he added, is an exhortation to “individual believers,” while the government’s duty is to enforce laws — in this case, strong border control policies to stop the influx of migrants into the United States.

In lectures to student groups he addresses across the country, Mr. Johnson has lamented: “There’s no transcendent principles anymore. There’s no eternal judge. There’s no absolute standards of right and wrong. All this is exactly the opposite of the way we were founded as a country.”

It is a viewpoint fervently embraced by much of the hard-right Republican base, which reveres Mr. Trump and identifies with his frequent claims of being persecuted, aggrieved and looked down upon by liberal elites.

On his podcast, which he co-hosts with his wife, Mr. Johnson often bemoans what he considers to be the repression of religious views in America.

“What we found was often the Christian viewpoint is not given equal treatment and equal platform and equal chance,” he said in one episode, according to transcripts of the shows compiled by the Brookings Institution. “Very often religious viewpoints, specifically Christian viewpoints, are censored and silenced.”

In the same episode, Mr. Johnson said the removal of religion from public schools had a “tragic effect,” adding: “People are separating what is religious, quote unquote, with quote unquote real life, right? And that dichotomy was never intended by the founding fathers.”

He said that sometimes “hostile” interviewers would ask him why he represented only Christians in his work as a lawyer doing religious liberty litigation, and not, say, Muslims or Jews.

“I would say because the fact is very simple: There is not an open effort to silence and censor the viewpoints of other religions,” he said. “It is only and always the Christian viewpoint that is getting censored.” He added, “The fact is the left is always trying to shut down the voices of the Christians.”

His colleagues on Capitol Hill describe Mr. Johnson as not particularly verbose or flamboyant, someone who lacks a flashy social media presence and may get lost in a sea of attention seekers. But his more mellow style can mask the fact that he proselytizes extremely hard-line views and has been hitting the right-wing talk show circuit doing that for decades.

In the 2000s, Mr. Johnson, then a lawyer and spokesman for the anti-abortion and anti-gay rights group Alliance Defense Fund, was also a prolific writer, posting columns to Townhall and writing opinion pieces for his local newspaper in Shreveport.

In his writings, he harshly criticized opponents on the left and those who did not share his beliefs. Almost always, the views he espoused were intertwined with his Christian beliefs.

In 2007, Mr. Johnson wrote a column claiming ulterior motives by proponents of the “Day of Silence,” an annual event where supporters pledge silence to bring attention to bullying and harassment of L.G.B.T.Q. students.

“The event is being sold to sympathetic schoolteachers and administrators as a gentle plea for sexual tolerance and understanding,” he wrote. “But the real agenda is to gild and glamorize homosexual behavior while gagging anyone who opposes it.”

“Experts project that homosexual marriage is the dark harbinger of chaos and sexual anarchy that could doom even the strongest republic,” he wrote in an article in 2004.

On Thursday, Mr. Hannity asked him to explain some of his previously stated views about same-sex marriage, which is broadly supported across the country, including among many Republicans.

“I don’t even remember some of them,” Mr. Johnson said of his previous comments. “I genuinely love all people, regardless of their lifestyle choices. This is not about the people themselves.”

Mr. Johnson’s political career has been a rare glide path that has put him in the most powerful position in Congress without ever having run a competitive race. When he took office in the Louisiana House of Representatives in 2015, he ran unopposed for a seat that had been vacated. In his first run for Congress in 2016, he handily defeated his Democratic opponent, Marshall Jones, and last year he ran unopposed for his seat.

He has also recorded over a thousand interviews on talk radio and television — much of it from his time at the Alliance Defense Fund, now called the Alliance Defending Freedom — leaving a long trail of words that help paint a picture of an arch-conservative who promotes a literal reading of the Bible.

In 2015, Mr. Johnson provided legal services to Answers in Genesis, a fundamentalist Christian group founded by Ken Ham that rejects scientific findings about evolution and the early history of the cosmos. The organization cites “the Word of God” in saying that the universe is 6,000 years old and suggests that “we simply have been indoctrinated to believe it looks old.” The universe is in fact about 13.8 billion years old, astronomers generally agree.

It retained Mr. Johnson after tourism officials in Kentucky refused to grant tax incentives for the building of a Noah’s Ark theme park, citing the organization’s plan to require employees to submit a statement of faith. Mr. Johnson successfully sued in 2015, arguing that the denial of tax breaks was discriminatory.

Mr. Johnson praised Ark Encounter, the theme park, which includes dinosaurs in its life-size replica of the ark, in a 2021 interview with Mr. Ham as he guest-hosted the radio show of Tony Perkins, the president of the Family Research Council, whom he has called his “original mentor.”

“The Ark Encounter is one way to bring people to this recognition of the truth that, you know, what we read in the Bible are actual historical events, and that there are implications to what you do with all these stories in the Bible there,” Mr. Johnson said.

Mr. Donalds, who ran unsuccessfully for speaker against Mr. Johnson this week, said Mr. Johnson’s decision to seek the position was about “being obedient to the Lord.” He said that was a good thing for House Republicans.

“You have a speaker who is not seeking the spotlight just to be in the spotlight,” Mr. Donalds said. “He’s answering a call.”

Benjamin Mueller contributed reporting.