Devin Nunes, the chairman of the House intelligence committee probing Donald Trump's Russia links, is to step down "temporarily".
Mr Nunes has been under pressure after announcing he went to the White House and met a secret source who provided him with information about leaks.
Democrats demanded the Republican remove himself from the investigations into Russian hacking during the election campaign and whether any of Mr Trump's team had contact with Moscow.
The Californian congressman said he felt forced to step down due to "entirely false" accusations filed against him with the office of congressional ethics.
He added that he wants to speak to the ethics office as soon as possible "to expedite the dismissal of these false claims".
Mr Nunes said it was in the best interest of the committee to have another Republican congressman, Mike Conaway, of Texas, temporarily take charge of the committee's investigation.
The House Ethics Committee said it was aware of the allegations that Mr Nunes "may have made unauthorised disclosures of classified information".
It added that it was determined to investigate the allegations.
US House Speaker Paul Ryan, the most senior Republican in the House of Representatives, said Mr Nunes still has his trust but he supports his decision to step aside.
The top Democrat on the intelligence committee, Adam Schiff, said that Mr Nunes' decision to stand aside provided an opportunity to move forward and that the investigation must get back on track.
The probe into Russian meddling and the Trump team's ties to the Kremlin had been effectively on hold after Mr Nunes refused to interview more witnesses until FBI Director James Comey and NSA chief James Clapper had returned for more questioning.
He wanted to quiz the pair on "additional information" that had come up but Democrats accused Mr Nunes of deliberately holding up the investigation.
Mr Trump has claimed allegations his administration has links to Russia are not an issue, but inquiries should be taking place into leaks from the White House.
His former national security adviser Michael Flynn was also forced to resign after three weeks in the job over allegations he had not told Vice President Mike Pence of his contacts with Russia, while Attorney General Jeff Sessions has had to recuse himself from decisions about Trump-Russia investigations because he too had meetings with a Moscow official.