The Japanese technology group also pledged to retain the existing management team and invest further in the business, increasing staff numbers outside the UK over the next five years.
The acquisition has seen shares in Arm valued at 1,700p – a premium of about 43 per cent on Friday’s closing level – with the company being priced at £24.3bn.
Arm’s technology is embedded in more than 95 per cent of smartphones, including Apple’s iPhone handsets. The company has more than 4,000 employees around the world.
Softbank chief executive Masayoshi Son said: “We have long admired Arm as a world-renowned and highly respected technology company that is by some distance the market leader in its field. Arm will be an excellent strategic fit within the SoftBank group as we invest to capture the very significant opportunities provided by the ‘internet of things’.”
He added: “This investment also marks our strong commitment to the UK and the competitive advantage provided by the deep pool of science and technology talent in Cambridge. As an integral part of the transaction, we intend to at least double the number of employees employed by Arm in the UK over the next five years.
“SoftBank intends to invest in Arm, support its management team, accelerate its strategy and allow it to fully realise its potential beyond what is possible as a publicly listed company. It is also intended that Arm will remain an independent business within SoftBank, and continue to be headquartered in Cambridge.”
Arm chairman Stuart Chambers said Softbank’s offer was “compelling” and would see the firm – founded in 1990 – “continue to play a key role in the development of new technology”.
“Arm is an outstanding company with an exceptional track record of growth,” he added.
“The board believes that by accessing all the resources that SoftBank has to offer, Arm will be able to further accelerate the use of Arm-based technology wherever computing happens.”