McNamara, 88, served as defense secretary to Presidents John Kennedy and Lyndon Johnson between stints as president of Ford Motor Co. and the World Bank.
He was introduced to the Italian-born Diana Masieri Byfield four years ago by mutual friends, shortly after she was widowed.
They will be married in the Basilica of St. Francis in Assisi, Italy, Sept. 16 in a private ceremony, the newspaper said.
He was married for 40 years to Margaret Craig, his teenage sweetheart, with whom he had two daughters and a son.
Byfield was married for more than three decades to Ernest Byfield, a former U.S. intelligence officer and public relations executive.
Byfield told the newspaper the subject of marriage came up earlier this year although McNamara never actually proposed, but rather secured the commitment with a series of hypothetical questions.