Following months of speculation, Microsoft announced that its new CEO is former enterprise and cloud boss Satya Nadella, with mobile firmly at the top of his agenda.

The appointment of Nadella as only the company’s third CEO in its almost 39-year history is effective immediately and sees him replace Steve Ballmer who announced in August that he would retire within 12 months.

One of Nadella’s priorities will be to address the struggles Microsoft has had in keeping pace with Apple and Google in the mobile space. The company’s Windows Phone operating system has yet to prove the viability of a third mobile ecosystem to rival Android and iOS.

But there have been some positive signs for Windows Phone and Microsoft is preparing to ramp up its mobile efforts with the acquisition of Nokia’s Devices & Services unit.

In his first email to Microsoft employees as CEO, Nadella wrote that it is a critical time for the industry and Microsoft and that “our job is to ensure that Microsoft thrives in a mobile and cloud-first world”.

“The opportunity ahead will require us to reimagine a lot of what we have done in the past for a mobile and cloud-first world, and do new things,” he added.

The 46-year-old joined Microsoft in 1992 and has led various divisions, including cloud services, server software, internet search and business applications. He was the driving force behind Microsoft’s move to cloud-based software.

Ballmer backed Nadella’s appointment, saying the company’s “passion and hunger for greatness will only grow stronger under Satya’s leadership”.

It was also announced that Microsoft co-founder and former CEO Bill Gates will relinquish his role as chairman of the board and assume a new role of technology adviser, in which he will support Nadella “in shaping technology and product direction”.

Gates, who will be replaced as chairman by lead independent director John Thompson, said “there is no better person to lead Microsoft than Satya Nadella” during “this time of transformation”.

“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,” he added.

Nadella’s name has been linked with the role for several months, although Ford CEO Alan Mulally initially emerged as favourite due to his turnaround credentials, established when Ford avoided a government bailout in 2009 under his leadership.

However, Mulally ruled himself out of the role early in January. Other external candidates were thought to include Ericsson CEO Hans Vestberg and the next CEO of Qualcomm, Steve Mollenkopf.

The shortlist was also reported to feature former Nokia CEO Stephen Elop, Skype boss Tony Bates and current Microsoft COO Kevin Turner.