He was sentenced to six months in prison for attempting to extort $2 million from the late-night host in exchange for keeping quiet about Letterman's affair with a staffer.
Halderman, 52, had originally pleaded not guilty in October but accepted a plea bargain. In addition to the jail time, he received 5 years of probation and 1,000 hours of community service.
"I have great remorse for what I have done," Halderman told the court.
Letterman attorney Daniel J. Horwitz said in a statement: "His admissions today were compelling, and for that he will receive a serious sentence." In his own statement, Letterman thanked the district attorney and New York City Police Department. "When they became involved with this case, I had complete faith that a just and appropriate result was inevitable," he said. "On behalf of my family, I am extremely grateful for their tireless efforts."
Halderman had lived with Stephanie Birkitt, a staffer on CBS's The Late Show with David Letterman, and learned about Birkitt's affair with Letterman, who is married with a young son.
When Halderman demanded $2 million not to go public with the information, Letterman went to the police. Halderman was arrested while trying to cash a fake check. Initially, his attorney had tried to build a defense claiming that his client was simply trying to market a screenplay to Letterman.
Letterman soon admitted his infidelity on the air, apologized to his wife and said his behavior was inappropriate, and even "creepy."
Manhattan District Attorney Cyrus R. Vance, Jr. commended Letterman for his cooperation – and for coming forward with the attempted blackmail plot. "By not giving in to the defendant’s extortionate demands for millions of dollars, and instead taking the courageous step of reporting the crime to law enforcement, Mr. Letterman risked the disclosure of certain aspects of his private life," he said in a statement Tuesday. "I commend Mr. Letterman for making the difficult but unquestionably right decision to report this crime to my office and thank him for his full and complete cooperation throughout the investigation and prosecution of the case."
Meanwhile, Halderman's friend Bob Arnot, tells PEOPLE that the former CBS News producer "feels great relief [after] they came forward with a deal which was a lot less draconian – a few months in jail and community service. [Halderman] is doing very well and he is optimistic and relieved it's a short sentence."
Reporting by Liz McNeil