Two pivotal witnesses — Fiona Hill, a former National Security Council official, and David Holmes, the political counselor at the US Embassy in Kiev — are set to testify Thursday in the impeachment inquiry on Capitol Hill.

Hill was present for a July 10 meeting at the White House in which US Ambassador to the European Union Gordon Sondland raised the prospect of probes into the 2016 presidential election and an energy company tied to Vice President Joe Biden’s son Hunter with high-ranking Ukrainian officials.

She has testified behind closed doors that her boss at the time, national security adviser John Bolton, instructed her to report the incident — which he likened to a “drug deal” — to the top lawyer on the NSC.

Holmes is the diplomatic staffer who went to lunch on July 26 in Kiev with Sondland, who called President Trump on his cellphone to discuss the “investigation” that the commander-in-chief wanted from Ukrainian President Volodymyr Zelensky.

The phone call took place a day after Trump urged Zelensky to launch investigations into the Bidens and and a debunked theory that Democrats conspired with Ukraine to interfere in the 2016 election.

In his deposition, Holmes said Sondland told him Trump only cared about “big stuff” that affected him, like what Holmes called the “Biden investigation” that the president wanted from Ukraine.

“So, he’s gonna do the investigation?” Holmes said he heard Trump ask. “He’s gonna do it,” Sondland replied, adding that he’d do “anything you ask him to.”

How to watch

The House Intelligence Committee will stream video on YouTube, and PBS will carry the hearings live, as will C-SPAN3, C-span.org and C-SPAN Radio.

Viewers can also watch the livestream on NYPost.com.

NBC, ABC and CBS plan to interrupt regular broadcasting with special reports on the hearings.

Fox News, CNN and MSNBC plan more extensive coverage, and several news sites will also livestream the proceedings, only the fourth time in US history that the House has held such hearings.

Hearing format

Committee Chairman Adam Schiff (D-Calif.) and Rep. Devin Nunes (R-Calif.), the top Republican on the panel, will have 45 minutes each to question witnesses at the beginning of each hearing.

Schiff and Nunes are expected to cede part of their time to Daniel Goldman, the committee’s director of investigations, and Steve Castor, GOP counsel for the House Oversight Committee.

The hearing will then move to questioning from individual members, alternating periods of five minutes between both parties. Schiff can add additional rounds at his discretion.

What comes next?

Hill and Holmes could be the final witnesses to appear, but Schiff hasn’t said definitively whether the Thursday hearing would end his portion of the process.

Once his panel concludes its work, action could then shift to the House Judiciary Committee, which would need to initiate and advance articles of impeachment to the full House.

Schiff and House Speaker Nancy Pelosi (D-Calif.) have not committed to a timetable — and also have suggested that impeachment isn’t a foregone conclusion but would depend on Schiff’s investigation.

If the Intelligence Committee decides to pursue articles of impeachment, the Republican-controlled Senate would hold a trial on the charges.