Pichot, capped 71 times by Argentina, is set to challenge Sir Bill in the election, due to take place during next month's World Rugby Council meeting.

Sir Bill, who declared his intention to run for a second term as chairman in January, had been widely expected to be re-elected unopposed at the May 12 meeting, which could be held remotely owing to concerns over the COVID-19 pandemic.

The 45-year-old Argentinian launched his chairmanship bid hours before the deadline for candidates to declare their intention to stand in the election.

Should Pichot succeed with his attempt to oust Sir Bill from the top job, he will become the first World Rugby chairman from outside Europe's Six Nations.

Pichot has served as a vice-president during the Englishman's first four-year tenure and said it was a "critical time and a critical election" for the worldwide governing body.

"The current crisis is an opportunity for the global realignment of our game," he said in a statement.

"We cannot miss it.

"It is time to align our global calendar and our strategic intent to attract the sustainable investment we need, or risk falling back to individual handouts or grants in the absence of a long-term vision for a global game."

Sir Bill had previously announced that he will be running with Bernard Laporte, President of the French Rugby Federation, as vice-chairman. 

Pichot had been elected as vice-chairman, along with Sir Bill, in 2016, when the English official stood unopposed to succeed Frenchman Bernard Lapasset as chairman.

Among the achievements Sir Bill highlighted in his announcement that he was standing again was the reintroduction of rugby to the Olympic programme at Rio 2016, when sevens made its debut, with Fiji winning the men's gold medal and Australia the women's.

He also pointed to a successful Rugby World Cup in Japan in 2019, which he claimed was "truly game-changing... igniting rugby growth in Asia".

Pichot has been the driving force behind the World League, an annual tournament which would have pitted six countries from the Northern Hemisphere against six from the South, with an in-built promotion and relegation system.

But the proposal was unanimously rejected by the Six Nations last June after the organisation raised concerns over the prospect of a relegation and promotion scenario.

"It is time to think of a sport where professional and commercial income is becoming a true benefit for all by empowering rugby's growth around the world and by moving on from the time where those benefits were just for a few," Pichot added.

"It is time to redefine the future of rugby, our game. 

"It is time to align rugby globally, moving forward as one, truly global game not falling back as lone unions or federations."