Washington DC - Tech billionaire Elon Musk spent at least $270 million to help Donald Trump win the presidency, according to new federal filings, making him the country's biggest political donor.

SpaceX and Tesla CEO Musk, the world's richest person, was an ardent supporter of Trump's White House campaign – funneling money into door-knocking operations and speaking at his rallies.

His financial backing, which has earned him a cost-cutting advisory role in Trump's incoming government, surpassed spending by any single political donor since at least 2010, according to data from nonprofit OpenSecrets.

The Washington Post reported that Musk spent more this election cycle than Trump backer Tim Mellon, who gave nearly $200 million and was previously the Republican's top donor.

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Musk donated $238 million to America PAC, a political action committee that he founded to support Trump, filings late Thursday with the Federal Election Commission showed.

An additional $20 million went to the RBG PAC, a group that used advertising to soften Trump's hardline reputation on the key voter issue of abortion.

Musk has been an ever-present sidekick for Trump since his election victory in November, inviting him to watch a rocket launch in Texas by his SpaceX company.

Trump has selected the South African-born tycoon and fellow ally Vivek Ramaswamy to head the so-called Department of Government Efficiency, through which the pair have promised to deliver billions of dollars of cuts in federal spending.

However, with Musk's businesses all having varying degrees of interactions with US and foreign governments, his new position also raises concerns about conflict of interest.

The president-elect has nominated several people close to Musk for roles in his administration, including investor David Sacks as the so-called AI and crypto czar.

Meanwhile, billionaire astronaut Jared Isaacman, who has collaborated with Musk's SpaceX, was named the head of US space agency NASA.