It emerged on Friday that Rinat Akhmetshin, a Washington lobbyist with dual citizenship, accompanied Russian lawyer Natalia Veselnitskaya to the June 2016 meeting, at which Trump Jr expected to receive secret information that would hurt Clinton in the 2016 election.
Several US media described Akhmetshin as former Soviet counterintelligence officer who is suspected by some US officials of having ongoing ties to Russian intelligence.
But the lobbyist rejected that allegation as "maliciously false," telling AFP he "never worked for any intelligence service."
The June 9 meeting has become the focus of allegations that the Trump election campaign collaborated last year with a covert effort by Moscow to turn voters away from Clinton.
Those allegations are currently under investigation by a high-powered Justice Department investigation led by former FBI chief Robert Mueller.
Emails showed that the meeting was pitched to Trump Jr, the eldest son of President Donald Trump, as a chance to obtain dirt on Clinton, allegedly supplied by the Russian government.
"If it's what you say I love it," Trump Jr said about the offer in an email to entertainment promoter Rob Goldstone, the person arranging the meeting.
The encounter was also attended by Trump campaign manager Paul Manafort and son-in-law Jared Kushner, underscoring how important the campaign apparently thought it could be.
One year on, emails showing the younger Trump's willingness to meet the lawyer are viewed in some quarters as a possible "smoking gun" in the ongoing federal investigation into whether Trump's campaign colluded with Russia to get the Republican elected.
'Designed to shift attention'
Accompanying Veselnitskaya at the meeting were Akhmetshin, an interpreter, and according to the Washington Post, Goldstone.
According to Akhmetshin, the Post reported, Veselnitskaya had said she had financial information on a US hedge fund with links to Clinton's Democratic Party, and left a document behind at the meeting.
But according to Trump Jr., Veselnitskaya did not produce damaging information on Clinton after all and instead focused the discussion on the US "Magnitsky" sanctions against a Russian company she represented.
Akhmetshin has also lobbied against the Magnitsky sanctions placed on a number of high-level Russian officials.
The Post also reported that Akhmetshin had served in the Russian military and may have worked in intelligence.
Akhmetshin flatly denied the suggestion that he had worked for a Russian spy agency.
"That claim is maliciously false and designed to shift attention from my campaign in Congress" against the Magnitsky law, he told AFP.
Trump Jr's lawyer, Alan Futerfas, told NBC News his client did not know any of the other people in the meeting beforehand.
"For the purpose of security or otherwise, the names were reviewed," he said.
