President-elect Joseph R. Biden Jr. will name Ron Klain, a veteran Democratic operative and a decades-long confidant, to be his White House chief of staff as early as Thursday morning, according to several people familiar with Mr. Biden’s decision.

Mr. Klain, a lawyer with deep experience on Capitol Hill, advising President Barack Obama and in corporate board rooms, has been seen for months as the likeliest choice to manage Mr. Biden’s team in the White House. Known for steady nerves, he also has a fierce wit, which he has frequently unleashed on President Trump on Twitter.

He was particularly critical of Mr. Trump’s handling of the coronavirus pandemic, having served as the “Ebola czar” under Mr. Obama during an outbreak of the deadly disease in his second term. A video of Mr. Klain lecturing Mr. Trump about the pandemic was widely seen during the campaign.