The meeting was first reported by the New York Times on Saturday and confirmed by an attorney representing Trump Jr.
The meeting was a chance for the envoy to offer help to the Trump presidential campaign, according to The New York Times.
The newspaper said the meeting, held on Aug. 3, 2016, was arranged by Erik Prince, the founder and former head of private military contractor Blackwater, who attended the meeting. Joel Zamel, a co-founder of an Israeli consulting firm, was also in attendance.
Alan Futerfas, Trump Jr.'s attorney, said on Saturday that nothing came of the meeting.
"Prior to the 2016 election, Donald Trump Jr. recalls a meeting with Erik Prince, George Nader and another individual who may be Joel Zamel," Futerfas said in an emailed statement. "They pitched Mr. Trump Jr. on a social media platform or marketing strategy. He was not interested and that was the end of it."
A company connected to Zamel also worked on a proposal for a "covert multimillion-dollar online manipulation campaign" to help Trump, utilizing thousands of fake social media accounts, the New York Times report said.
The envoy, Lebanese-American businessman George Nader, told Trump, Jr. that the crown princes of Saudi Arabia and the UAE were eager to help his father win the 2016 presidential election, the paper said.
Since 1974, the United States has barred foreign nationals from giving money to political campaigns and it later barred them from donating to political parties. The campaign financing laws also prohibit foreign nationals from coordinating with a campaign and from buying an ad that explicitly calls for the election or defeat of a candidate.
The Saudi and UAE embassies in Washington did not immediately respond to requests for comment.
The Wall Street Journal last month reported that investigators working for U.S. Special Counsel Robert Mueller had met with Zamel, and that Mueller's team was looking into his firm's work and his relationship with Nader.
Mueller is investigating whether Russia meddled in the presidential election and if Moscow colluded with the Trump campaign, as well as whether Trump committed obstruction of justice by trying to thwart the U.S. Department of Justice probe.
Trump has denied any collusion with Russia and has called the Mueller investigation a "witch hunt."
The New York Times report said the meetings are an indication that other countries besides Russia may have offered help to Trump's presidential campaign. Mueller's investigators have questioned witnesses in Washington, New York, Atlanta, Tel Aviv and elsewhere regarding possible foreign help to the campaign, the report said.
Peter Carr, a spokesman for Mueller's team, declined to comment on the report.
Zamel's attorney, Marc Mukasey, said in a statement to Reuters that his client "offered nothing to the Trump campaign, received nothing from the Trump campaign, delivered nothing to the Trump campaign and was not solicited by, or asked to do anything for, the Trump campaign."
"Media reports about Mr. Zamel's engaging in 'social media manipulation' are uninformed," Mukasey added. "Mr. Zamel's companies harvest publicly available information for lawful use."
Kathryn Ruemmler, Nader's lawyer, told the paper that her client "has fully cooperated with the U.S. special counsel's investigation and will continue to do so."
Erik Prince, who is also the brother of U.S. Education Secretary Betsy DeVos, could not be immediately reached for comment.