He said Trump's "narcissism" means he would be unable to accept losing the GOP nomination race.
Barr is a former Trump loyalist, who has recently turned against his ex-boss.
Former Attorney Bill Barr said that Donald Trump would seek to destroy the Republican Party if defeated in his bid to become its 2024 presidential nominee.
In an op-ed in The New York Post published on Tuesday, Barr addressed Trump's announcement last week that he was seeking the Republican Party candidacy for the White House in 2024.
He said that if Trump loses the nomination, it could tear the GOP apart.
"Unless the rest of the party goes along with him, he will burn the whole house down by leading 'his people' out of the GOP," Barr said, referring to the former president's hardline supporters in the party.
"Trump's willingness to destroy the party if he does not get his way is not based on principle, but on his own supreme narcissism," Barr wrote.
"His egoism makes him unable to think of a political party as anything but an extension of himself — a cult of personality."
Trump's status as the GOP's most powerful figure has taken a hit in the wake of the midterm elections, when several of the high profile candidates he'd endorsed in key races were defeated.
Barr is among Republicans claiming the the divisive and flawed candidates Trump endorsed are the reason for the party's failure to win control of the Senate, and to only secure a small House majority.
"The GOP's poor performance in the recent midterms was due largely to Trump's mischief," said Barr, citing his candidate choice, failure to provide proper funding, and stoking of internal GOP divisions.
His criticisms is strikingly similar to that of Trump's niece, Mary Trump, who also believes that the former president would seek to "burn everything down" if Republicans blame their midterms defeat on him.