Education and Sports Minister Hakubun Shimomura, the Government official in charge of overseeing preparations for the Games, claimed Mori had given his informal consent to take over.

Full details of the Organising Committee are due to be announced by the Tokyo Metropolitan Government and Japanese Olympic Committee (JOC) on January 24. 

Masato Mizuno, who had led Tokyo's successful bid which saw them beat rivals Istanbul and Madrid, was not considered for a lead role in the Organising Committee as he said he was not interested.

Mori had initially turned down the opportunity to lead Tokyo 2020 because he claimed, at the age of 76, he was too old. 

JOC President Tsunekazu Takeda welcomed Mori's decision to change his mind.

"It will formally be decided in discussions of three parties, including Tokyo. Mori-san is someone of distinguished service who was instrumental in the Tokyo bid. I think he is suitable," said Takeda.

Mori is currently the President of the Japanese Rugby Football Union (JRFU) and closely involved in preparations for the 2019 World Cup, which is being held in the country for the first time.

It is not clear whether he will retain his position with the JRFU or step down to concentrate on Tokyo 2020.

Yoshirō Mori had been closely involved in Tokyo's campaign to host the 2020 Olympics and Paralympics, including representing them at London 2012 ©Getty Images

There will be mixed feelings about Mori's appointment, however.

He served as Japan's Prime Minister between April 2000 and 2001.

But he left office with a reputation as one of the country's most unpopular leaders with his approval rating in single digits following a series of gaffes.

The most controversial of these came in February 2001 when, after receiving the news that an American submarine had accidentally hit and sunk a Japanese fishing ship during an emergency surface drill, resulting in the death of nine Japanese, he continued playing a round of golf.

Nevertheless, JOC senior director Tsuyoshi Aoki claimed Mori's appointment was a boost for Tokyo's preparations for 2020.

"We are not at the final stage of rendering the decision, but it is reassuring that Mori-san has accepted," he said.

"He is someone who knows sports himself [as a rugby player].

"I think that he understands many things."

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