Jean-Paul Delevoye, the French government official whose controversial pension reform plans have triggered nationwide strikes, resigned on Monday over his failure to declare outside income.

The High Commissioner for Pensions decided to leave "on his own initiative" according to the Elysee.

"President [Macron] recognises his personal commitment and his work on the pension reform," the Elysee statement added. "His withdrawal allows the clarification of the situation."

Pressure started to build after it was reported that Delevoye, 72, had failed to disclose 13 remunerated or volunteer activities on his declaration of interest filed two months after he entered government.

Article 23 of the French Constitution prevents government workers from holding other remunerated activities.

Among these were administrative roles for the Parallaxe thinktank — for which he was paid more than €5,000 a month — as well as for the French Federation of Insurers and for the charitable arm of railway operator, SNCF.

According to the AFP news agency, these different activities paid him at least €123,000 since he was tasked by President Emmanuel Macron of devising the pension reform in September 2017. Delevoye had said he would reimburse the sum.

But the political scandal erupted at a particularly sensitive time as the pension reform, officially unveiled last week by Prime Minister Edouard Philippe, has led to widespread protest and severe disruptions on the country's transport system.

Jean-Luc Melanchon, leader of the far-left La France Insoumise party, who had been calling for Delevoye's resignation since the media reports were first published, welcomed his departure on Monday, adding that "his reform must also go."

Marine Le Pen, at the helm of the far-right Rassemblement National, also hailed the announcement.

"Delevoye's position, weakened by repeated lies and potential conflicts of interest, was untenable," she wrote on Twitter.

Lawmakers from the ruling La Republique En Marche (LREM) party have, however, rallied behind their "Mister Pension" with Gilles Le Gendre, President of LREM in the National Assembly, writing on Twitter that the party's MPS express their "sadness and respect for the courageous decision he has just taken."

"Nothing and no one will remove from him that he thought of and designed the fairest and most protective reform in France since 1945," he added.

The task of finding a someone to replace Delevoye, who crafted and therefore know the contentious reform better than anyone, will be particularly arduous for the government which has so far refused to compromise despite the protest.

The pension reform aims to simplify the current regime, which has 42 different schemes for workers depending on their profession, and to push back the "pivotal age" of retirement — the age from which retirees get their full pension — from 62 to 64-year-old.

The points-based system would instil a "minimal pension" of €1,000 and keep guarantees for workers in "tiring jobs", allowing them to leave work two years earlier, Philippe said last week.

But some protesters decry the end of special regimes they have until now benefitted from as well as the increase in the pivotal age, which they criticise as a way to raise the retirement age.