Inspired by a true story, as they like to say in Hollywood, the film traces the fleeting ups and frightening downs of Chris Gardner, whose efforts to keep his family from sinking into poverty evolve into a life-and-death struggle of social Darwinian proportions. It’s the early 1980s, and while Ronald Reagan is delivering the bad economic news on television, Chris is about to prove you don’t need an army to fight the war on poverty, just big smiles and smarts, and really sturdy shoes. (It also helps that the star playing him is as innately sympathetic as Will Smith.)

Given how often Chris breaks into a run on the streets of San Francisco, it’s a good thing his shoes are well built; his lungs, too. Written by Steven Conrad and directed by Gabriele Muccino, “The Pursuit of Happyness” recounts how Chris, plagued by some bad luck, a few stupid moves and a shrew for a wife, Linda (Thandie Newton), loses his apartment and, with his 5-year-old, Christopher (Jaden Christopher Syre Smith, Mr. Smith’s own beautiful son), joins the ranks of the homeless, if not the hopeless. Evicted from the mainstream and bounced from shelter to shelter, Chris holds firm to his dignity, resolve, faith, love and independence. His optimism sweeps through the film like a searchlight, scattering clouds and dark thoughts to the wind.

It’s the same old bootstraps story, an American dream artfully told, skillfully sold. To that calculated end, the filmmaking is seamless, unadorned, transparent, the better to serve Mr. Smith’s warm expressiveness. That warmth feels truthful, as does the walk-up apartment Chris’s family lives in at the start of the film, which looks like the real paycheck-to-paycheck deal. As does the day care center, which is so crummy it can’t even get happiness right (hence the title).

Money matters in “The Pursuit of Happyness,” as it does in life. But it matters more openly in this film than it does in most Hollywood stories that set their sights on the poor, largely because Chris’s pursuit of happiness eventually becomes interchangeable with his pursuit of money. He doesn’t want just a better, more secure life for himself and his child; either by scripted design or by the example of the real Chris Gardner, he seems to yearn for a life of luxury, stadium box seats and the kind of sports car he stops to admire in one scene. His desires aren’t just upwardly mobile; they’re materialistically unbound. Instead of a nice starter home, he (and the filmmakers) ogles mansions. It’s no wonder he hopes to become a stockbroker.

That may sound like a punch line, at least to some ears, but it’s the holy grail in “The Pursuit of Happyness.” A self-starter, Chris has sunk all of the family’s money into costly medical scanners that he tries to sell to doctors and hospitals. But the machines are overpriced, and the sure thing he banked on has landed them in debt. Forced to work two shifts at a dead-end job, Linda angrily smolders and then rages at Chris, which seems reasonable since he has gambled all of their savings on an exceptionally foolish enterprise. (And, unlike her, he hasn’t signed up for overtime.) But this is a film about father love, not mother love, and Linda soon leaves the picture in a cloud of cigarette smoke and a storm of tears.

Chris and the filmmakers seem happy to see her go, but life only gets tougher once she and her paychecks disappear. Much of the film involves Chris’s subsequent efforts to keep himself and his child housed and fed while he is enrolled in an unpaid internship program at a powerful stock brokerage firm. Bright and ferociously determined, Chris easily slides into this fantastical world of shouting men, ringing phones, gleaming surfaces and benevolent bosses. He goes along to get along, and when one of his bosses asks for money to pay for a cab, he quickly opens his wallet. Chris himself stiffs another working man for some money because that wallet is so light. But this is a film about him, not the other guy.