The co-founder of the £4bn British tech firm Darktrace, Poppy Gustafsson, has been appointed as the government’s new investment minister.

Darktrace, the listed cybersecurity company, was this month sold to a US private equity firm and Gustafsson stepped down as chief executive. She will become a peer.

Ministers had been trying to appoint someone to the crucial job for months. Ben Wegg-Prosser, who founded the Global Counsel advisory firm with the Labour grandee Peter Mandelson, turned the job down.

The government said Gustafsson would head the Office for Investment as a minister in the Treasury and the Department of Business and Trade. She will also preside over a new unit drawn from those departments and No 10, plus a new external advisory board.

Keir Starmer said: “I am delighted to welcome Poppy Gustafsson OBE as our new investment minister – an accomplished entrepreneur who brings invaluable experience to the role.

“We’re upgrading the Office for Investment to ensure it is fit for purpose and has the capability it needs to make the UK the first choice for investment and the best place in the world to do business, which is central to our mission to drive growth and make people better off.”

Gustafsson, one of the best-known figures in the UK tech industry, founded Darktrace in Cambridge in 2013 with backing from the late billionaire Mike Lynch’s Invoke Capital.

Like many of Darktrace’s management and key staff, Gustafsson, who co-founded the firm when she was 30, was a former employee at Lynch’s software company Autonomy.

The 59-year-old Lynch and six others died last month when a superyacht sank off the coast of Sicily in a storm.

Darktrace’s time as a publicly listed company has been dogged by controversy and a number of short-sellers. Analysts have criticised the business model as sales over substance.

Some of the criticism, which led to Darktrace’s share price plummeting to record lows, prompted Gustafsson to publish a 1,200-word defence of the company last year in which she said it was run with the “greatest integrity”.

Gustafsson is expected to join the prime minister at a council of nations and regions meeting on Friday.