A federal lawsuit filed in Manhattan claims that Mr Trump’s campaign “gleefully welcomed Russia’s help”.
The Democratic National Committee (DNC) alleges that top Trump campaign officials conspired with the Russian government and its military spy agency to hurt Hillary Clinton and tilt the election in Mr Trump’s favour by hacking Democratic Party computers.
The President’s campaign has dismissed the case as frivolous and predicted it will be dismissed in due course.
Russia “mounted a brazen attack on American democracy”, the DNC claims, alleging that thousands of documents and emails were extracted from DNC computers in the hack.
The suit also names Donald Trump Jr., Mr Trump’s son-in-law Jared Kushner, and Mr Trump associate Roger Stone as defendants.
Allegations of Russian interference, and possible collusion by the Trump campaign, are being investigated by special counsel Robert Mueller.
Mr Trump has denied that his campaign colluded with Russia, while Russia has denied election meddling.