After serving for two years in the United States Army, Younger obtained his Juris Doctor degree from New York University Law School in 1958.
After several years in the U.S. Attorney's office, Younger opened a practice as a private defense lawyer, partnering with his wife and handling a wide variety of cases.
In 1974, Younger resigned from his judgeship to move upstate, accepting a professorship (the Samuel S. Leibowitz Professor of Trial Techniques) at Cornell Law School.
He was a well-known lecturer to audiences of lawyers and law students, and more than thirty years after his death, tapes of his continuing legal education talks remain in frequent use, prized for their wit and theatrics as well as their substance and insight.
A selection of his writings, including his article, "The Trial of Alger Hiss", originally published in Commentary (August 1975); the story behind the case of Erie Railroad v. Tompkins; and the obscenity prosecution of James Joyce's book Ulysses were collected in an anthology: The Irving Younger Collection: Wisdom & Wit from the Master of Trial Advocacy, published by the American Bar Association in 2011.