Paul Newell said it first occurred to him that he should try to unseat the Assembly speaker on primary day in 2004.

Blaming Speaker Sheldon Silver for thwarting an overhaul of the Rockefeller drug sentencing laws — “possibly the most destructive piece of legislation on the books,” Mr. Newell said — he had looked forward to voting against the speaker.

His polling station, however, was closed because Mr. Silver, as usual, had no opponents. “I was thinking that somebody ought to challenge this guy,” Mr. Newell said. Two election cycles later, Mr. Newell has quit his job as an AIDS awareness organizer for a South African NGO and is campaigning full-time against Mr. Silver, who represents a diverse district that encompasses the Lower East Side, Chinatown, and Wall Street.

“I need to get a few thousand people to vote for me,” he said. “Sheldon Silver is a very powerful man in Albany. He’s not that powerful downtown.”

Mr. Newell is running on two issues: accountability and “affordable” housing, both of which, he said, Mr. Silver is against.

He accuses the speaker of “blocking development of ‘affordable’ housing in downtown for 20 years” and also blames him for “killing” congestion pricing, an issue, he said, that is “the perfect demonstration of Sheldon Silver’s contempt for the democratic process and the concerns for Lower Manhattanites.”

A spokesman for Mr. Silver’s campaign, Jonathan Rosen, said, “Assemblyman Silver is focused on delivering results on the issues that matter for Lower Manhattan residents, ‘affordable’ housing and increasing aid for New York City schools.”

Next month, Mr. Newell will turn 33 — about the same age Mr. Silver was when he was first elected to the Assembly in 1976.

The speaker was last opposed in a party primary in 1986 when a man named John Bal tried to beat him and lost with 20% of the vote.

“I am not another John Bal,” Mr. Newell said.

He has hired a campaign manager, Evan Hutchison, a grassroots campaigner for General Wesley Clark and Senator Kerry in the 2004 presidential race. And he’s prepared to tap into personal funds. He feels confident, however, that voters across the state will fork over cash once he informs them the identity of his opponent. “There are millions of people in this state who don’t like Sheldon Silver. Some of them use the Internet and some of them answer phone calls,” he said.

His headquarters is a wooden desk under a loft bed in a rent-stabilized tenement apartment on Division Street that he shares with two roommates. Mr. Newell describes himself as a jovial Jewish guy and resembles Wood Allen, but with wire-rimmed glasses and shorter hair. He’s unmarried and owns a 9-year-old gray tabby named Zot — a jazz homage to an Armstrong scat.

He doesn’t drive, but cruises the city on a mountain bike that he painted red. His favorite movie and book are Mel Brooks’s “The Producers” and Ralph Ellison’s “Invisible Man.”

Mr. Newell, whose mother was a copywriter for a variety of trade publications and whose father is a telecommunications lawyer, grew up on East 10th Street, outside Mr. Silver’s district. He attended Stuyvesant High School, the most competitive public school in the city, but began a “young and irresponsible” phase, dropping out during his sophomore year. “I was not properly applying myself,” he said. He transferred to the alternative City-as-School High School — where internships substitute for class work and where “a third of the kids were pregnant or young mothers,” he said — and then enrolled in Whitman College on the West Coast as a history major.

In Washington State, he landed his first paid political job, a field organizer for what would be the final campaign of Rep. Tom Foley, the U.S. House speaker whose defeat in 1994 has ironically given Mr. Newell confidence in retrospect. “It taught me that a sitting speaker of a legislative body can be beaten in his home district,” he said.