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Uber wants to be the world’s private driving service. Now the company is amassing the war chest to do it.

The start-up closed a new $1.2 billion round of financing on Thursday, with investors valuing the company at a staggering $40 billion.

That puts a new mountain of cash on top of the $1.5 billion that Uber had already raised. And it may collect even more: Uber may eventually sell an additional $600 million in stock, and it is working with Goldman Sachs to sell, potentially, another $1 billion in debt to some of the Wall Street firm’s wealthy private clients.

Uber’s ascent is one of the most rapid by a start-up in years. Five years ago, Uber was just an app that allowed customers to summon a private car with the push of a smartphone button. Since then, it has surged in growth to surpass even other members of Silicon Valley’s exclusive 11-digit club — start-ups whose valuations exceed $10 billion.

With the additional money, Uber is setting itself up for what its investors hope will be the next mammoth initial public offering, following in the footsteps of Facebook and the Chinese e-commerce company Alibaba Group.

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The new money, however, comes in the face of a rash of fierce criticism about the company’s approach to users’ privacy. While people briefed on the fund-raising process said that the recent controversy did little to diminish enthusiasm among investors, Uber acknowledged on Thursday that it had more growing up to do.

Raising yet more cash is another step in Uber’s plan to become the world’s premier logistics service, capable of transporting people to places they want to go as quickly and seamlessly as possible. The company has also signaled its ambitions to be a one-stop shop for delivering anything, anytime, anywhere — even groceries — perhaps one day rivaling the likes of Amazon, eBay and Google, all of which run nascent delivery services.

“Millions of people may decide that they no longer need to own a car because using Uber will be cheaper than owning one,” Travis Kalanick, Uber’s chief executive, wrote in a blog post on Thursday announcing the new round of funding.

Accomplishing that goal will require huge amounts of both capital and chutzpah. In every new market, the company must wage battles with existing taxi and limousine industries, curry favor with local regulators and persuade local drivers to switch en masse to Uber’s service.

It is a series of battles that are not easily, or cheaply, fought.

“There’s an entire thriving transportation ecosystem that’s being disrupted here,” said Susan Shaheen, a professor at the University of California, Berkeley who studies civil engineering and transportation companies. “Start-ups like Uber are up against the taxi companies, the charter party carriers, not to mention the shuttle industry. We’re in early days here.”

Uber is by far the car-ride start-up with the largest footprint. In the last year, it has expanded to more than 250 cities in 50 countries. The company, which is privately held, does not disclose its revenue, but said in its blog post that it is six times as large as it was one year ago, and its growth is accelerating.

When the latest fund-raising round is included, Uber is valued at $41.2 billion — or more than Standard & Poor’s 500 components like CBS and the grocery chain Kroger.

Besides taxis and limousines, the company faces stiff competition on other fronts.

It is up against Lyft — a competitor that offers a similar ride service and is also backed by big investors — in a race to conquer major American cities like New York and San Francisco. Lyft, which announced the appointment of new senior executives on Thursday, is competing fiercely to lure drivers, passengers and engineering talent away from Uber.

Uber must also square off against Hailo, an Uber-like app for summoning taxis that has focused much of its efforts in Europe. And it will face fights in Southeast Asia, where GrabTaxi already hosts more than 60,000 drivers on its ride-hailing platform.

That is most likely where Uber will be spending a significant chunk of its newfound riches. In the fund-raising announcement, Mr. Kalanick said Uber planned to make “substantial investments, particularly in the Asia Pacific region,” where it is already facing regulatory scrutiny in Thailand, Singapore and Vietnam.

Should the start-up need even more money, it will probably have no problem collecting additional cash. According to a corporate filing in Delaware on Thursday, the company may raise an additional $600 million in stock in its latest financing round. The Delaware filing, obtained by VC Experts, was reported earlier by Fortune.

More intriguing is the private sale of convertible debt that Uber has hired Goldman to run. The terms of the offering, as described by people briefed on the matter, give the company an incentive to go public within the next few years. The securities being offered to Goldman’s clients can be converted into stock — at a discount of roughly 20 to 30 percent of Uber’s valuation in an initial stock offering.

If Uber does not go public within four years, the interest rate that the company pays out on those securities will rise, these people added.

Yet those fistfuls of cash cannot solve all of the start-up’s problems — notably, its own culture.

In recent weeks, Uber has been at the center of a series of privacy scandals that have tarnished its image. Critics deplored the company’s ethics when Emil Michael, an Uber executive, suggested that Uber conduct “opposition research” on journalists who write unflattering stories about the company.

Another employee, Josh Mohrer, is facing unspecified disciplinary action for looking up the travel data of a BuzzFeed reporter.

Last month, Senator Al Franken, Democrat of Minnesota, sent a letter to Uber asking the company to explain in detail how it treats the private travel data of its users.

In the blog post on Thursday, Mr. Kalanick, Uber’s chief, pledged to work on those issues.

“The events of the recent weeks have shown us that we also need to invest in internal growth and change,” he wrote. “Acknowledging mistakes and learning from them are the first steps.”