Edward Durr Jr., a Republican who this month toppled New Jersey’s second most powerful lawmaker, had three children under 13 when a mortgage company began foreclosure proceedings on his 1,200-square-foot, one-story home in South Jersey in 1997.

Within two years, he and his first wife had filed for bankruptcy, identifying $64,784.99 in debts to J.C. Penney, an insurance company and a bank, court records show.

“My kids didn’t really know what was going on,” said Mr. Durr, who dropped out of high school when his father, a self-employed carpenter, got sick and needed help at work. “We kind of sheltered them from that.”

Two decades later, New Jersey’s high property taxes and cost of living would become centerpieces of Mr. Durr’s campaign, cementing his improbable win against Steve Sweeney, a Democrat who had held a near-final say over all legislation in Trenton as president of the State Senate.

A commercial truck driver, he describes himself as a “blue-collar, Christian, Second Amendment supporter.” He is a strong backer of former President Donald J. Trump, who called to congratulate him on his win, and an opponent of vaccine and mask mandates and what he calls government “tyranny.”

Mr. Durr’s victory and the region’s strong Republican turnout are considered emblematic of evaporating enthusiasm for Democrats in suburban and rural areas and wide dissatisfaction with President Biden. That mix contributed to a Republican win in Virginia and Gov. Philip D. Murphy’s unexpectedly close re-election in New Jersey, and is seen as an ominous sign for the Democratic Party ahead of next year’s congressional midterms.

“If anything, my election showed nobody’s untouchable,” Mr. Durr said.

During the campaign, Democratic operatives used mailers and a video ad to highlight Mr. Durr’s past financial troubles, but he won by about 2,300 votes anyway, pulling off one of the biggest political upsets in state history.

“Not for nothing,” said Steve Kush, a Republican consultant who worked with Mr. Durr’s campaign, “but those kinds of attacks actually backfired this time. There’s a lot of other people going through some very hard times. Who hasn’t had problems with financing?”

Since the Nov. 2 election, Mr. Durr, 58, has become a mini-celebrity, unable to walk through Walmart or ShopRite or pick up chicken wings from his local pub, Wilson’s, without being asked to pose for a selfie.

He does not take office until Jan. 11. But he is already using a new domain name, edthetrucker.com, to raise funds for re-election and hawking “Ed the Trucker” hats, “Riding DURRty” bumper stickers and “Dangerous Durr” T-shirts and mugs, co-opting a term Mr. Murphy used to describe him.

His campaign flew so far under the radar that it was not until after Election Day that a reporter for WNYC, a public radio station, publicized incendiary comments he had made on Twitter that disparaged the Muslim Prophet Muhammad and called Islam a “false religion.”

On the day Mr. Sweeney conceded, Mr. Durr met with Muslim leaders at a masjid near his campaign headquarters, reiterating his public apology for the comments and offering a commitment to “stand against Islamophobia and all forms of hate.”

“As long as you know somebody, it’s hard to hate somebody — don’t you think?” he told reporters gathered outside, holding a Quran given to him during a two-hour meeting with members of the state’s Council on American Islamic Relations. “It’s very easy to hate somebody that you don’t know.”

At home in Logan Township, 15 miles outside Philadelphia, Mr. Durr himself remains largely unknown. He did not win a majority of votes in the Democrat-led town where he lives near the Delaware River, in an area known as Repaupo.

In Penns Grove, where the three-bedroom, one-bath house he lost in foreclosure last sold for $22,000, neighbors said they had not heard of him before Election Day, if at all.

“He didn’t win his own town,” said Frank Minor, Logan’s Democratic mayor. “That tells you a lot right there.”

“He’s been anti-Muslim, anti-vax,” Mr. Minor added. “He’s a Trump Republican. That’s what he is. That’s what he’s going to do.”

Rural and predominantly white, southern New Jersey is one of the most conservative parts of the state. Democrats in Mr. Durr’s district outnumber Republicans, yet Mr. Trump narrowly won more votes than his Democratic opponent in 2016 and in 2020.

Buoyed by Mr. Sweeney and the influence of George E. Norcross III, a well-connected political boss, Democrats controlled most local and state offices. That also changed on Election Day.

Mr. Durr’s two Republican running-mates ousted incumbent Democrats in the Assembly, and Republicans flipped two seats on the Gloucester County Board of Commissioners, the legislative body where Mr. Sweeney cut his political teeth.

Mr. Durr said he shed 55 pounds during the campaign, weight loss he attributed to walking and knocking on doors in places Republicans seldom consider competitive: Mr. Sweeney’s hometown, West Deptford, and the city of Bridgeton, a tight-knit enclave of mostly Latino immigrants.

“People were, like, shocked,” Mr. Durr said. “They’d say, ‘Nobody’s ever been here.’”

Mr. Durr said he hoped to keep his job as a truck driver for the Raymour & Flanigan furniture chain, and the health insurance it provides, even after he is sworn in as a senator, a part-time position that pays $49,000. Lawmakers who took office after 2010 are not eligible for health coverage.

He rides a 2012 Harley-Davidson motorcycle, spoils his three pit bulls — “I call them my fur babies” — and, with his five siblings, takes care of his mother, a recent widow who lives next door.

Before joining the furniture company, he worked in construction and said he often held multiple jobs, including making pastries for Dunkin’ Donuts and working in a farm supply store. During two growing seasons, he drove trucks for East Coast Sod and Seed.

“He was on time,” said Andy Mottel, the manager of the Pilesgrove, N.J., farm, which transports sod across the country and provides the field grass for Yankee Stadium. “He worked every day. He has that strong voice — very knowledgeable about sports.”

Mr. Durr completed his G.E.D. through Gloucester City High School, and he has made no secret of his unease with his sudden stardom. (“I feel like I’m about to throw up,” he said the day Mr. Sweeney conceded.) He will be a member of the minority party in the State House, making it unlikely he will have significant power to steer or stonewall legislation.

When ticking off his legislative priorities, he mentions goals like “bringing jobs here, bringing businesses here,” and he is the first to say he has a lot to learn about how Trenton works. “If it’s an issue that concerns New Jersey citizens, I’m going fight for it,” he said.

It was his fourth campaign for public office. He ran for State Assembly as an independent in 2017 and as a Republican in 2019, and he ran last year for Logan Township council.

It is unclear how much he spent to win. The latest financial reports show he spent roughly $2,300, but he has said that the final figure will be between $5,000 and $10,000.

New Jersey has some of the strictest gun control laws in the country, and Mr. Durr said he originally decided to run for public office after learning he could not get a license to carry a concealed weapon.

“I’ve been on every military base as a truck driver on the East Coast,” he said. “Why am I being refused my right to self-protect? The Second Amendment says I have a right to self-protect.”

Mr. Durr’s Islamophobic remarks in 2019 were not his only controversial comments on social media.

He also appeared to equate public acquiescence to pandemic-related mandates to remaining silent during the Holocaust. After a violent racist rally in Charlottesville, Va., in 2017, he offered comments reflecting the legitimacy of “both sides,” a position similar to Mr. Trump’s initial response.

Officials with the Islamic council said that they worried that Mr. Durr’s past hate speech, left unchecked, could lead to violence. During the meeting at the masjid, they offered him examples of relatives who had been targeted for being Muslim.

Three people who participated said that he was engaged and appeared genuine in his desire to learn more about the Muslim faith. The group shared snacks, and Mr. Durr observed a 10-minute prayer service.

“He was open minded,” said John Starling, the imam of a mosque in Cherry Hill, N.J. “He was without hesitation ready to make the situation right.”

Atiya Aftab, who teaches in the Middle Eastern Studies program at Rutgers University and also attended the meeting, said she understood it as the start of an ongoing conversation.

“I’m not second-guessing his intent,” Professor Aftab said. “I did feel that it was genuine and authentic. But ultimately it’s actions that will speak louder than words.”

Camille Furst contributed reporting and Susan C. Beachy contributed research.