The spending figures, first reported by the New York Times, are expected to appear in a federal filing due on Thursday. They surpass Musk's contributions to the 2024 presidential election, when he sank nearly $300m into Donald Trump's re-election campaign.
The spending reasserts the SpaceX and Tesla chief executive as the top Republican mega-donor and extends his rightwing political influence. Musk previously led the Trump administration's efforts to cut federal agencies before a dramatic falling out with the former president, and has in recent years become a central figure for far-right political movements internationally.
The donations also mark a sharp reversal. In the middle of last year, Musk claimed he would step back from large-scale political giving, after the failures of his so-called "department of government efficiency", a costly public backlash to his political influence, and his rift with Trump appeared to dampen his interest in Washington politics.
According to Reuters and the New York Times, Musk's money is spread across a series of political action committees, including his own America Pac. His largest single contribution was $158m to the Senate Leadership Fund, a Super Pac working to help Republicans retain control of the Senate. He has also given $76m to America Pac, $20m to the Congressional Leadership Fund Republican Super Pac, and $10m to the Republican Governors Association.
Musk gave $10m to a Pac supporting Ken Paxton, the Republican Senate candidate in Texas, who faces Democratic nominee James Talarico in a closely watched race. Another $10m went in January to Nate Morris, a Kentucky Republican Senate candidate who withdrew from the race in May after accepting an offer to become US ambassador to Colombia.