James O'Donnell, 47, was arrested and charged with driving while intoxicated after a May 23 accident in Holbrook in which Kristen Iacono, 26, of East Setauket, was seriously injured, authorities said.
Iacono died a day later, district attorney spokesman Robert Clifford said Friday.
Police said O'Donnell was headed north on Holbrook Road in his 1995 Mercury Marquis when he hit Iacono's car at the intersection of Holbrook and the north service road of the Long Island Expressway.
O'Donnell pleaded not guilty to the initial DWI charge and remains held on bail.
As a result of Iacono's death, Clifford said more serious charges are "likely" after the case is presented to a grand jury.