Kellyanne Conway becomes campaign manager and Stephen Bannon of Breitbart News the CEO. Paul Manafort remains as campaign chairman.
Donald Trump told AP the new leaders were “terrific people… they’re champs”.
The Republican presidential candidate has seen his poll ratings slip since the GOP conventions last month.
Donald Trump trails rival Democratic Party candidate Hillary Clinton both nationally and in key battleground states.
The latest shake-up comes just 82 days before the election.
Speaking to Associated Press news agency about Stephen Bannon, executive chairman of the politically conservative news and opinion website Breitbart, and pollster Kellyanne Conway, Donald Trump said: “I’ve known both of them for a long time. They’re terrific people, they’re winners, they’re champs, and we need to win it.”
AP said the details of the new hierarchy were hammered out at a lengthy senior staff meeting at Trump Tower on August 16 and that more senior appointments were expected in the coming days.
An article in Bloomberg in October 2015, described Stephen Bannon as “the most dangerous political operative in America”.
Stephen Bannon says his role at Breitbart is “virulently anti-establishment”.
Kellyanne Conway has previously worked for Republican politicians Dan Quayle and Newt Gingrich.
Although Paul Manafort stays in his job, analysts say the new appointments, which come two months after campaign manager Corey Lewandowski was sacked, represent a demotion.
The Washington Post cited Donald Trump campaign aides as saying the Republican candidate respected Paul Manafort but felt “boxed in” by people “who barely knew him”.
Paul Manafort, a former adviser to George H.W. Bush and Bob Dole, only joined the Trump campaign in March.
Donald Trump has been pressed by some Republicans to tone down his fiery rhetoric in the wake of a number of controversial comments in the past two weeks and the subsequent drop in poll ratings.
However, Donald Trump appears to want to stand by the campaign style that won him the Republican nomination.
He said on August 16: “You know, I am who I am. It’s me. I don’t want to change.
“Everyone talks about, <<Oh, well you’re going to pivot, you’re going to>>. I don’t want to pivot. I mean, you have to be you. If you start pivoting, you’re not being honest with people.”
Paul Manafort has had a troubled week, following a report in the New York Times that ledgers in Ukraine showed he was earmarked for $12.7 million in undisclosed cash payments from the former pro-Russian government between 2007 and 2012. He denied receiving any “off-the-books cash payment”.
The Trump team’s alleged pro-Russia links have been a key issue of the campaign, and the latest allegations sparked a call from the Clinton campaign for a full disclosure.
Opinion polls since the national conventions have made grim reading for the Trump team, both nationally and in key states.
The national lead for Hillary Clinton is currently between seven and eight points, the polls suggest.
The New York Times said on August 15 that no modern candidate trailing by this much three weeks after the conventions had won the election.
An opinion poll in the state of Virginia, carried in the Washington Post on August 16, gave Hillary Clinton a 14 point lead there.
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