PA /PA Archive/Press Association Images
Purnell, the BBC's director of strategy and education, will have his remit broadened to radio when the division's existing chief, Helen Boaden, announces her retirement.
The Daily Telegraph first reported the story. A BBC source also confirmed to Business Insider that an announcement is imminent.
Purnell has little programming experience and his background as a senior politician will raise concerns about whether the BBC's radio unit can be impartial under his watch.
Purnell was the work and pensions secretary in former prime minister Gordon Brown's government. He also served as the culture secretary during a nine-year tenure as an MP.
Rumours about the radio role have been circulating for some time - and have already caused concern among some Tory politicians. Damian Collins, the acting chair of the Culture, Media and Sport Committee, told the Financial Times last month that his appointment would be "unprecedented."
"I can't think of any other example of a former politician running such a major part of the BBC's programming. Because of his political background there will undoubtedly be questions about impartiality," he said.
Purnell was hired by BBC director general Tony Hall in 2013 as director of strategy and digital. He is one of Hall's key lieutenants and has been instrumental in steering the broadcaster through negotiations to renew its royal charter for another 11 years.
The Telegraph said the BBC is aware of the concerns Purnell's appointment might raise. It reported that he was interviewed for the radio post by senior independent directors on the BBC's board. The broadcaster will also bring in an "experienced editorial figure to carry out the day-to-day management of the radio division" alongside Purnell.
The Telegraph added that culture secretary Karen Bradley has "decided against raising any concerns with the corporation."