SEATTLE — Microsoft Corp.’s board has chosen longtime company executive Satya Nadella to guide the faltering software giant into the future amid the rise of mobile computing and as competitors Google, Amazon.com and Apple increasingly threaten its relevance.

Nadella will assume the role of chief executive officer and join Microsoft’s board immediately.

The company also announced that Bill Gates, formerly board chairman, will assume the title of founder and technology adviser, which Microsoft said will allow him to devote more time to the company and to support Nadella in shaping technology and product direction. Gates remains a board member.

John Thompson, lead independent director, will become board chairman.

Nadella becomes only the third CEO in Microsoft’s 39-year history, following in the footsteps of co-founder Gates and current CEO Steve Ballmer, who announced in August that he would be retiring within 12 months.

“During this time of transformation, there is no better person to lead Microsoft than Satya Nadella,” Gates said in a news release. “Satya is a proven leader with hard-core engineering skills, business vision and the ability to bring people together. His vision for how technology will be used and experienced around the world is exactly what Microsoft needs as the company enters its next chapter of expanded product innovation and growth.”

“The opportunity ahead for Microsoft is vast, but to seize it, we must focus clearly, move faster and continue to transform,” Nadella said in a news release. “A big part of my job is to accelerate our ability to bring innovative products to our customers more quickly.”

In an email to employees, Nadella said: “We are hungry to do more. Our industry does not respect tradition – it only respects innovation. This is a critical time for the industry and for Microsoft. … Our job is to ensure that Microsoft thrives in a mobile and cloud-first world.”

As CEO, Nadella will lead a global behemoth that last fiscal year brought in $78 billion in revenue and $22 billion in profit. It has more than 100,000 employees worldwide. Another 32,000 Nokia employees are expected to join the payroll once that acquisition closes.

Nadella, 46, is a 22-year Microsoft veteran and currently heads its Cloud and Enterprise group, which provides servers, cloud platforms and other technology tools for corporations. “Cloud” is the term used to refer to services and data that live on remote servers and which users access online.

Last fiscal year, his division pulled in $20.3 billion in revenue and $8.2 billion in operating income.

Described as very smart, personable, charismatic and collaborative, Nadella is well respected within the company and well regarded by Wall Street. Some investors, though, who would like to see more radical changes at Microsoft, question whether an insider such as Nadella will bring about big changes.

Nadella will be heading a company in the middle of great transitions.

The company still has formidable strengths, including its pervasiveness among corporations, its dominant position in PC operating systems and in productivity software, and its rapidly growing business providing services and technology infrastructure via online networks.

It’s also made a big investment in recent years on building its cloud infrastructure and services. But it’s the daunting challenges facing Microsoft that the new CEO will have to quickly address.

While Microsoft built its fortune on making its Windows operating system ubiquitous on PCs, the market for PCs has declined. In its place, the markets for smartphones and tablets have soared – and in those markets, Microsoft has very little share.

The introduction last year of Windows 8, which featured a radical new user interface designed to be especially touch-friendly, met with a tepid response. And it’s only now that a full array of touch-screen devices featuring the new operating system, at better prices, are reaching the marketplace.

While Apple’s devices and Google’s services and Android operating system have succeeded with consumers, Microsoft has struggled in that market, the Xbox console being the glaring exception.

Microsoft is also in the middle of a huge organizational transition.

The company is shifting toward becoming one that produces devices and provides services through online networks – the “devices and services” vision that Ballmer first announced last year.

It will soon become one of the largest device manufacturers in the world, when its $7 billion purchase of Nokia’s handset business is finalized, expected sometime early this year.

And the “services” side of its “devices and services” vision has been growing rapidly, with offerings such as Office 365 on a rapid adoption rate.

The company is still in the middle of a huge reorganization that Ballmer began in the summer, designed to spark better collaboration between groups and a quicker pace for updates and innovations.

Microsoft’s share price finally began to rise last year, after remaining stubbornly flat for much of the decade. The most recent big stock price increase came after Ballmer announced he would be retiring.

Ballmer has faced criticism for years about Microsoft’s stagnant stock price and its slip behind competitors such as Apple and Google in the fast-growing mobile market.