The person requested anonymity to discuss the private appearance before the grand jury.
Pence's appearance on Thursday before a grand jury in Washington scrutinising the president he once loyally served is a milestone in the Justice Department's investigation and likely gives prosecutors a key first-person account about certain conversations and events in the weeks preceding the deadly January 6, 2021, insurrection at the US Capitol.
It also carries significant political implications, coming as Pence hints at entering the 2024 presidential race and a potential run against Trump, the Republican frontrunner.
The testimony came hours after a federal appeals court in a sealed order rejected a bid by Trump's lawyers to block Pence's appearance.
Pence was subpoenaed to testify earlier this year, but Trump's lawyers objected, citing executive privilege concerns. A judge in March refused to block Pence's appearance, though he did side with the former vice president's constitutional claims that he could not be forced to answer questions about anything related to his role as presiding over the Senate's certification of votes on January 6.
"We'll obey the law, we'll tell the truth," Pence said in an interview with CBS News' "Face the Nation" that aired on Sunday.
"And the story that I've been telling the American people all across the country, the story that I wrote in the pages of my memoir, that'll be the story I tell in that setting."
Pence, a former Indiana governor and congressman, has said that Trump endangered his family and everyone else who was at the Capitol that day and history will hold him "accountable".
Lawyers for Pence had raised their own, more narrow challenge to the subpoena. They argued that because Pence was serving in his capacity as president of the Senate as electoral votes were being counted in Congress on January 6, he was protected from being forced to testify about that process under the Constitution's "speech or debate" clause, which is intended to protect members of Congress from being questioned about official legislative acts.
A judge agreed with that argument, effectively narrowing the scope of his expected testimony.
The Justice Department special counsel leading the investigation, Jack Smith, has cast a broad net in interviews and has sought the testimony of a long list of former Trump aides, including former White House counsel Pat Cipollone and former adviser Stephen Miller.
Smith is separately investigating Trump over the potential mishandling of hundreds of classified documents at his Palm Beach, Florida estate, Mar-a-Lago, as well as possible efforts to obstruct that probe.
On Wednesday, Trump's lawyers in that investigation called the Department of Justice investigation "severely botched" and "politically infected" and urged the House Intelligence Committee to step in by holding hearings and introducing legislation to correct classified document handling procedures in the White House and to standardise procedures for presidents and vice presidents for when they leave office.
"DOJ should be ordered to stand down, and the intelligence community should instead conduct an appropriate investigation and provide a full report to this Committee, as well as your counterparts in the Senate," the lawyers wrote.
It is unclear when either of the special counsel's investigations will end or who, if anyone, will be charged.
