DiFiore resigned as district attorney after the state Senate unanimously affirmed her nomination by Gov. Andrew Cuomo to lead New York's highest court.
A special election will be held on Nov. 8 to elect a new Westchester DA.
DiFiore served as district attorney since 2006.
In a statement, McCarty said, “It has been an absolute honor to serve under Janet DiFiore during her tenure as the Westchester County District Attorney. There is no one serving in the public sector that I hold in higher esteem.."
"I look forward to leading the excellent staff she has assembled over the coming year," McCarty said.
Before becoming acting district attorney, McCarty served as the chief of trial operations, overseeing all trials in the superior and local courts in Westchester.
As an assistant district attorney since 1980, McCarty was the deputy division Chief of the Superior Court Trial Division for six years.
McCarty has tried more than 100 cases, including the successful prosecutions of Carolyn Warmus -- the so-called "Fatal Attraction" murder case -- and serial killer Patrick Baxter. McCarty is a graduate of the University of Rochester and Albany Law School.
On Dec. 1, 2015, Gov. Cuomo, a resident of New Castle, nominated DiFiore after months of speculation that DiFiore was a leading candidate for the opening on the Court of Appeals. Cuomo faced a deadline to name a successor for Chief Judge Jonathan Lippman, who reached the mandatory retirement age of 70..
DiFiore was among seven candidates for the opening. Only one other woman has served as chief judge: the late Judith Kaye who died on Jan. 7 at the age of 77. She was a native of Monticello.
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