WASHINGTON—A federal judge ruled that former Vice President Mike Pence must testify before a grand jury about conversations he had with former President Donald Trump before Jan. 6, 2021, rejecting executive privilege claims by Mr. Trump, people familiar with the ruling said.
In a sealed ruling Tuesday, Judge James Boasberg said that while Mr. Pence isn’t immune from testifying about any illegal conduct by Mr. Trump, the former vice president can decline to answer some questions relating to his role as president of the Senate during the certification that day of President Biden’s victory, according to one of the people.
Judge Boasberg’s ruling, which can be appealed, came less than a week after he held a closed-door hearing on the matter.
Mr. Pence told reporters last month that he would challenge the subpoena calling for his testimony, issued by special counsel Jack Smith, “if needs be to the Supreme Court.”
The ruling is the latest in a number of wins for the special counsel. Earlier this month, another federal judge in Washington found that Mr. Smith’s team had presented enough evidence that Mr. Trump may have misled his own lawyers about his post-White House retention of classified documents to compel one of them, Evan Corcoran, to testify. Mr. Corcoran appeared before the grand jury for about three hours on Friday.
Mr. Smith is leading the Justice Department probe into the efforts of Mr. Trump and his allies to overturn his 2020 presidential election loss, as well as the inquiry into Mr. Trump’s handling of classified documents.
A spokesman for the Justice Department declined to comment.
Mr. Pence opposed the subpoena on the grounds that, as vice president, he served also as president of the Senate—a role that enables him to invoke a constitutional protection that generally shields members of Congress from being questioned about their legislative activities.
Judge Boasberg took over earlier this month as chief judge for the U.S. District Court for the District of Columbia. In that role, he oversees all grand jury matters in the court, including Mr. Smith’s investigations.
The Washington grand jury looking into the handling of the Mar-a-Lago documents and Jan. 6 is separate from the Manhattan grand jury investigating Mr. Trump’s role in a hush-money payment to a porn star, which is coming closer to voting on a potential indictment of the former president.
Two senior advisers to the former vice president, Mr. Pence’s chief of staff, Marc Short, and legal counsel Greg Jacob, provided testimony in the Jan. 6 investigation under subpoena last year.
Prosecutors have sought information about a Jan. 4, 2021, Oval Office meeting where conservative lawyer John Eastman pushed Mr. Pence, in Mr. Trump’s presence, to block the counting of Electoral College votes.
At the time, Mr. Trump had embraced a fringe theory advanced by Mr. Eastman that the vice president could reject electors from certain states or suspend the counting of votes in order to turn the matter back to those states, and publicly and privately pressured Mr. Pence to embrace that position.
Mr. Pence saw any effort to interfere as illegal, a view backed by constitutional law scholars.
Mr. Pence was a target of the mob of Mr. Trump’s supporters that stormed the Capitol on Jan. 6, 2021. Mr. Trump sent out a tweet at 2:24 p.m. that day saying, “Mike Pence didn’t have the courage to do what should have been done.”
Mr. Pence, who helped shore up support with Christian evangelicals for Mr. Trump in 2016, is traveling the country and expected to enter the presidential contest soon.