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Donald J. Trump added another reinforcement to his delegate-wrangling operation on Monday with the hiring of Ken McKay, the former campaign manager for Gov. Chris Christie of New Jersey, to help lead his effort to secure the Republican presidential nomination.

Mr. McKay is the latest longtime political insider to join Mr. Trump’s campaign as he makes a final push to win the 1,237 delegates needed to become the nominee. He recently hired Paul Manafort to be his convention manager, and Rick Wiley, who was Gov. Scott Walker’s campaign manager, as an adviser.

“He will support our delegate operations team and bolster our ground-game efforts,” Mr. Trump said of Mr. McKay in a statement. “He brings tremendous experience to the job, and I know he is up to the task of working with my team.”

The new hire comes as Mr. Trump’s two remaining rivals, Senator Ted Cruz of Texas and Gov. John Kasich of Ohio, have teamed up in an effort to make it harder for the Manhattan businessman to win the remaining states.

Mr. McKay was previously chief of staff of the Republican National Committee, serving until he resigned in 2010 after it emerged that the national party spent thousands of dollars at a California sex club. He went on to serve as political director for the Republican Governors Association and was also an adviser to the presidential campaign of Gov. Bobby Jindal of Louisiana.

“I am very honored to have the opportunity to work with Mr. Trump and such a resilient campaign,” Mr. McKay said. “There is no question that he is the presumptive nominee, and will unify our party to take back the White House in November.”