“He had the right connections but trod the path and the slippery pole like everyone else,” said Richard Harris, another British fund manager who met Mr. Rees-Mogg through a Hong Kong conservatives’ group. “He had no easy ride to politics.”

Margaret Brewer, a local Conservative Party official in North East Somerset, recalled that party leaders made repeated calls warning her and the other local representatives not to select him. “It was made quite clear that was not what they wanted in a candidate,” she said. Ms. Brewer was not deterred, though, and neither was Mr. Rees-Mogg. “Jacob doesn’t care what people think,” she said. “He must do,” she added. “But he doesn’t seem to.”

In Parliament, Mr. Rees-Mogg fell to the far right of the Tory spectrum, opposing climate change legislation and increased spending on welfare benefits and supporting tax breaks for bankers and corporations. In an interview, he said the Tory party must win a “battle of ideas” between the forces of the free market and socialism, and that its message to voters, especially young ones, had been too timorous.

“I think that conservative principles have a broad appeal and you should state them boldly, and the point of a Conservative election is to do conservative things, not to do Labour things but slightly less damaging,” he said. Voters today, he said, were drawn to politicians with more pointed views, both on the left and right, “because the centrist approach didn’t succeed.”

Mr. Rees-Mogg’s gentle, erudite manner made him a favorite among his fellow lawmakers, even those repelled by his ideas. But only with “Brexit” did the populist mood swing fully in his direction. Attributes that once made Mr. Rees-Mogg an unviable candidate — like his opposition, as a conservative Roman Catholic, to abortion under any circumstances — now make him look brave and honest, wrote Freddy Gray, deputy editor of The Spectator.

In the age of social media, Mr. Gray added, a comic persona also comes in handy. “It’s all part of the LOL, nothing matters, Twitter thing,” he said in an interview. “It’s dangerous, in a way, that if you don’t make yourself an obviously comical figure, or seem like you’re on the fringes, people will regard you with suspicion.”

As the Conservative Party conference approached — it begins on Sunday, and Mr. Rees-Mogg is expected to give as many as nine speeches in two days — moderate Conservatives sent up flares of warning. One of his colleagues in Parliament said she would quit the party if he became leader (though she added that she found him “incredibly charming”). Matthew Parris, a prominent columnist and former Conservative member of Parliament, warned that for a party struggling to modernize, elevating Mr. Rees-Mogg “would be pure hemlock.”