WASHINGTON — Vice President Mike Pence has hired a personal criminal defense lawyer to guide him through the various investigations encircling the White House, an aide said on Thursday.

Mr. Pence has retained Richard Cullen, a former United States attorney for the Eastern District of Virginia, becoming one of the most prominent figures in the Trump administration to have taken on personal white-collar criminal defense counsel.

Mr. Pence, who had little relationship with the president before joining the campaign ticket just before last July’s Republican convention, is most likely a peripheral figure in the government’s inquiry into Russia’s interference in the election and potential collusion with members of the Trump campaign. Paul Manafort — Mr. Trump’s former campaign chairman who has been scrutinized for financial ties to a pro-Russian political party — was instrumental in recruiting Mr. Pence.

But as the special counsel investigation progresses — focusing increasingly on the president himself and his actions in office — the vice president’s account as a possible witness may become more relevant.