On the eve of a legal battle in New York, Wayne LaPierre told board members on Friday that he would step down as the longtime chief of the National Rifle Association.

Mr. LaPierre, 74, has led the organization for more than three decades. But his resignation came as he faced his gravest challenge yet, a corruption trial in Manhattan amid a legal showdown with New York’s attorney general, Letitia James. Jury selection has already begun and opening arguments were scheduled for early next week.

The announcement, which is effective on Jan. 31, is not part of a deal with the attorney general’s office. Andrew Arulanandam, Mr. LaPierre’s longtime spokesman, will become the interim chief executive. The development was first reported by The Wall Street Journal.

This is a developing story and will be updated.