Even in television news, a little stunt casting can’t hurt.

MSNBC turned heads on Wednesday when, minutes before the House impeachment hearings got underway, the network announced a surprise guest: George T. Conway III, the conservative lawyer and husband of President Trump’s White House counselor, Kellyanne Conway.

Little known outside legal circles before his wife’s ascent to political stardom, Mr. Conway has become a liberal sensation by emerging as an unlikely critic of the president. His Twitter account, once a sleepy province of corgi and cat videos, is now a favorite of Trump detractors eager for Mr. Conway’s sweeping and spiky denunciations.

But while Mr. Conway has also ventured onto newspaper op-ed pages (“Trump is a racist president” was the headline of his Washington Post opinion piece in July) and other media forums, he had drawn the line at appearing on Mr. Trump’s favored medium. Until now.

“I don’t, frankly, want to be on television,” Mr. Conway said during the Wednesday morning broadcast from the MSNBC set in New York, where he had been granted a perch across from the co-anchors Brian Williams and Nicolle Wallace. “But this,” he added, referring to Mr. Trump’s conduct, “I just don’t get why people can’t see this, and why people are refusing to see this. It’s appalling to me.”