Gov. Chris Christie of New Jersey endorsed Donald J. Trump on Friday, a major turn in a wild race and one that gives the New York businessman a major boost as he heads into the pivotal "Super Tuesday" contests.

Mr. Christie was a candidate for president himself until he came in sixth place in New Hampshire's primary. Seeing his political career facing an abrupt conclusion after his failed presidential campaign, he expressed his anger Friday at Senator Marco Rubio, who he was said to be upset with, blaming the "super PAC" backing the Florida senator for halting his momentum in New Hampshire with a string of slash-and-burn ads.

The endorsement came a day after Mr. Rubio, in a withering debate performance, turned his guns on Mr. Trump for the first time, and followed up with his attacks on Friday morning, calling Mr. Trump a "con artist."

At Friday's news conference announcing the endorsement, which was peppered with demeaning insults of Mr. Rubio by the two men, Mr. Christie repeatedly attacked Mr. Rubio, calling his behavior at the debate "desperate" and reflective of a "losing campaign."

Mr. Trump welcomed the endorsement with warm praise for the New Jersey governor.

"He's been my friend for many years, he's been a spectacular governor," said Mr. Trump, standing with Mr. Christie at a news conference in Fort Worth for the endorsement.

He then turned on Mr. Rubio, saying that at the debate, he saw Mr. Rubio backstage with "a pile of makeup," he said. "I said Marco, easy with the makeup, you don't need that much."

Mr. Christie, noting he has been friends with Mr. Trump for a decade, said that he was "proud to be here to endorse Donald Trump."

Mr. Trump "will do exactly what needs to be done to make America a leader around the world again," he said.

But his backing of Mr. Trump comes after weeks of him saying that it was time for the "entertainment" portion of the race to end, and as he had said that the type of executive leadership that a governor has is important.

Mr. Christie's endorsement augments Mr. Trump's appeal for working-class voters. But more significantly, Mr. Christie could become a catalyst for other leading Republicans to back him after they have held back from supporting the developer despite his recent string of victories.

Mr. Trump heaped praise on Mr. Christie for tenderizing Mr. Rubio during the final debate in New Hampshire, where the Florida senator wilted under blistering criticism from the governor.

"I thought he was gonna die — good going, Chris," Mr. Trump said.