Three years ago, when Ibram X. Kendi was up for the National Book Award, he thought he had no chance.

He was a little-known assistant professor at the University of Florida. His book, “Stamped From the Beginning,” a sweeping history of nearly five centuries of racist thought in America, had received admiring but sparse reviews.

“Before we walked over to the dinner, my wife asked me if I had written a speech,” Dr. Kendi recalled in an interview last month. “I hadn’t, but I wrote out a few notes just in case. When they called my name, I was shocked.”

It was barely a week after the 2016 election, and Dr. Kendi — at 34, among the youngest ever to win the nonfiction award — made his way onstage to deliver an eloquent speech nodding at the man just elected president, and paying tribute to “the human beauty in the resistance to racism.”

Since then, he has given a lot more speeches — 46 so far this year alone. He has become one of the country’s most in-demand commentators on racism, and leads the new Antiracist Research and Policy Center at American University, which recruited him as a full professor after the award.

It’s been a wild and fast ride to the top of his profession, with one terrifying detour thrown in. Midway through writing his new book, “How to Be an Antiracist,” out on Aug. 13, Dr. Kendi received a diagnosis of Stage 4 colon cancer, which has a five-year survival rate of about 12 percent.

A recent scan, taken a year after he completed both chemotherapy and surgery, came back all clear. But Dr. Kendi — who turns 37 on publication day — isn’t taking anything for granted.

“I was pretty disciplined and determined before the diagnosis, but now I’ve taken it to a whole other level of seriousness,” he said. “Even though I’m young, I can’t imagine I have so much time. It forced me, compelled me, to take risks.”