Grossman met the Taliban representatives in late January, an unnamed Afghan official confirmed on Wednesday.
"I can confirm that Mr. Grossman met with the Taliban representatives in Qatar," the official said.
Following his meeting with the Taliban, Grossman briefed Afghan President Hamid Karzai about his negotiations with the militants during the Afghan leader’s visit to Italy.
American and Taliban officials have secretly negotiated for more than a year about the so-called peace talks.
During the negotiations, the US gave the Taliban the opportunity to open an office in Qatar and agreed to release high-ranking Taliban prisoners.
Afghan President Hamid Karzai accepted the US proposal to let militants establish an office outside Afghanistan under pressure from the White House.
Meanwhile, the Afghan High Peace Council has warned no foreign power should engage with the Taliban without Afghanistan's consent and that the office should only be used to conduct negotiations.
The US-led war on Afghanistan was launched under the pretext of toppling the Taliban regime. A decade and after failing it its objectives, the White House has now decided to negotiate with the militant group.