Natalia Veselnitskaya met with Donald Trump Jr and the President’s son-in-law Jared Kushner at Trump Tower in June last year.
The meeting was reported in the New York Times on Saturday.
Mr Trump Jr said on Sunday that he had attended the meeting because he believed it would give him information helpful to his father’s campaign.
Before that admission he said the meeting was concerned with a US-Russia adoption law.
Mark Corallo, a spokesperson fro Mr Trump’s legal team, said President Trump was also not aware of the meeting and did not attend.
Paul Manafort, Mr Trump’s campaign chief at the time, was also present during the meeting.