On the computer in Philip Roth’s Upper West Side apartment these days is a Post-it note that reads, “The struggle with writing is over.” It’s a reminder to himself that Mr. Roth, who will be 80 in March and who has enjoyed one of the longest and most celebrated careers in American letters, has retired from writing fiction — 31 books since he started in 1959. “I look at that note every morning,” he said the other day, “and it gives me such strength.”

To his friends the notion of Mr. Roth not writing is like Mr. Roth not breathing. It sometimes seemed as if writing were all he did. He worked alone for weeks at a time at his house in Connecticut, reporting every morning to a nearby studio where he wrote standing up, and often going back there in the evening. At an age when most novelists slow down, he got a second wind and wrote some of his best books: “Sabbath’s Theater,” “American Pastoral,” “The Human Stain” and “The Plot Against America.” Well into his 70s, the books, though shorter, came uninterruptedly, practically one a year.

But over the course of a three-hour interview — his last, he said — Mr. Roth seemed cheerful, relaxed and at peace with himself and his decision, which was first announced last month in the French magazine Les InRocks. He joked and reminisced, talked about writers and writing, and looked back at his career with apparent satisfaction and few regrets. Last spring he appointed Blake Bailey as his biographer and has been working closely with him ever since.