Smith has been at Fox News since its founding in 1996. He was among the first people hired by Fox News’ co-founder, the late Roger Ailes, for the network’s launch. His recent tenure, however, has been marked by conflict and criticism, not just from Trump but from within the network itself.

The internal tensions at Fox News appear to have contributed to his resignation, according to multiple people at the network and those close to Smith. Smith was also in the middle of a long-term contract, making his resignation – and Fox’s agreement to release him – highly unusual.

Earlier this month, he engaged in an extraordinary war of words with Tucker Carlson, one of the network’s most popular opinion hosts.

Smith called Carlson “repugnant” for not defending Fox News legal analyst Andrew Napolitano when a guest on Carlson’s programme called Napolitano “a fool” for criticising Trump’s efforts to gain damaging information on Democratic rival Joe Biden from the president of Ukraine.

Carlson fired back, clearly referring to Smith but not naming him: “Unlike maybe some dayside hosts, I’m not very partisan.”

A former Fox News staffer who has recently been in touch with Smith said the spat with Carlson was the last straw and that Smith had grown frustrated in recent months by the repeated attacks on the news division by other opinion hosts. Fox News declined to comment on the reasons for Smith’s resignation.

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In farewell remarks, Smith said: “Recently I asked the company to allow me to leave Fox News and begin a new chapter. After requesting that I stay, they graciously obliged. The opportunities afforded this guy from small-town Mississippi have been many. It’s been an honour and a privilege to report the news each day to our loyal audience in context and with perspective, without fear or favour.”

Smith has often incurred the wrath of some loyal Fox News viewers with his sceptical reporting and commentary on the US president, in stark contrast to its prime-time and morning hosts, who often flatter the leader. Trump has given frequent interviews to his most loyal Fox News personalities but has never sat for one with Smith.

Smith’s criticism of Trump dates to the beginning of Trump’s presidency. After a presidential news conference in early 2017, for example, he called some of Trump’s responses “absolutely crazy”. He went on to defend rival news network CNN after Trump called its reporting “fake news”.

“CNN’s reporting was not fake news,” Smith said at the time. “Its journalists follow the same standards to which other news organisations, including Fox News, adhere.”

More recently, he urged Fox News viewers to read special counsel Robert Mueller’s report of his investigation into Russian meddling in the 2016 election, strongly suggesting that it didn’t exonerate the president, as Trump and Attorney General William Barr had claimed. “Everyone in America should read” it, he said on the air. “Everyone.”

Trump, in turn, has sometimes disparaged Smith by name on Twitter, viewing him as an apostate at a network he believes should be loyal to him.

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While complaining about a new Fox News poll showing a majority of Americans favor his impeachment, Trump on Thursday tweeted: “@FoxNews is ... much different than it used to be in the good old days.” He named Smith as one of the people at Fox News who “doesn’t deliver for US anymore. It is so different than it used to be. Oh well, I’m President!”.

In August, Trump referred to Smith as “low ratings Shep Smith”, calling him “hopeless and clueless”. And in a tweet earlier that month, he wrote, “watching Fake News CNN is better than watching Shepard Smith, the lowest rated show on @FoxNews. Actually, whenever possible, I turn to @OANN”, a small cable-news competitor.

According to Nielsen Media Research, Smith’s programme dominated its time period, outdrawing competing programs on MSNBC and CNN by 48 per cent and 81 per cent, respectively, during the third quarter. His programme attracted an average of 1.28 million viewers during the period. However, it was often the lowest-rated daytime programme in Fox News’ lineup.

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Smith’s departure coincided with reports this week that Barr travelled to New York to meet with Fox Corp Chairman Rupert Murdoch at Murdoch’s home in New York City. Neither side explained the reason for the meeting.

Asked by reporters on Friday for his reaction to Smith’s resignation, Trump responded with mock sympathy. “Is he leaving?” he said. “Oh, that’s a shame ... Is he leaving because of terrible ratings? If he’s leaving, I assume he’s leaving for bad ratings ... Well, I wish him well.”

In his final broadcast on Friday, the 55-year-old Smith said he had struck an agreement with Fox News in which “I won’t be reporting elsewhere at least in the near future”, an apparent reference to a “non-compete” agreement that keeps departing TV news personalities from joining competitors. He did not announce any plans other than spending time with family and friends. “Then we’ll see what comes along,” he said.