When award-winning author Erik Larson sets out to write historical nonfiction, he allows the characters to be his guide. For Mr. Larson, the subjects of his books are not just historical figures you might find in a textbook, but individuals full of life, contradiction and depth.

“Because of the way I like to do history, I look for the people that we can hold hands with when we’re going through whatever it is I’m writing about,” he said.

Mr. Larson’s latest book is The Splendid and the Vile, a New York Times bestselling biography of Winston Churchill, his family and London during the Blitz of World War II. On Sunday evening, Mr. Larson addressed a crowd of over 1,000 participants for the second virtual event of this year’s Martha’s Vineyard Author Series. He was joined by fellow best-selling author and seasonal resident of the Vineyard, Amor Towles.

The Splendid and the Vile was published in February. It tells the story of Churchill’s first year in office at the height of German’s bombing campaign against the United Kingdom. But beyond the facts and events, the book touches on an even larger story—that of human resilience in turbulent times.

“[There was] this healing ability to adapt and persevere, which really was so striking to me throughout my research,” Mr. Larson told the audience on Sunday. “There’s a wonderful adaptability to people, even under stress.”

Though always curious about the Blitz, Mr. Larson said the inspiration for the book struck him after moving to New York city a few years ago and witnessing the long-lasting impact of 9/11 on the city and its natives.

“Given how 9/11 affected us, [I thought] how on earth did people in London endure 57 consecutive nights of bombing…and then another six months of intensifying raids,” he said.

In the book, Ms. Larson gets at these questions by examining prominent historical figures, like Churchill and President Roosevelt. But the story truly comes to life through the narratives of lesser-known characters, like the prime minister’s 17-year-old daughter Mary, a favorite of Mr. Larson’s.

“She commented on world events in a very smart and very perceptive way. But also she was, after all, a 17-year-old girl who loved to have fun. Her diary is peppered with all these wonderful references that really get to the core of how you survive an ordeal like the Blitz. And one way was snogging in the hayloft,” he said with a laugh.

Drawing from private diaries and public documents, Mr. Larson weaves diverse storylines of war generals and everyday people, from the German Luftwaffe fighter pilot, Adolf Galland, to Churchill’s private secretary, Jock Colville.

“[The stories are] a metaphorical encapsulation of what happened to the common man during that period.”

The final effect is a vivid picture of life, at once sensational and mundane in war-time London.

Mr. Towles then turned the conversation to the topic of Mr. Larson’s research process. Mr. Larson said he conducted most of his research for the book tucked away in the archives. For him, physically engaging with the material is a priority.

“Those moments when you have tactile contact with something really important from the past are something that really sustain you through the work,” he said. “When you start to feel history vibrate through an object, it’s very powerful.”

In the question and answer segment, viewers asked a range of questions about Mr. Larson’s career and future plans. One participant asked how Mr. Larson felt after completing such an intricate and heavily researched book.

“[Normally] I can get sort of a postpartum depression when I finish a book,” he said. “But in this case, I was not depressed at all. I was so thrilled.”

The event is still available for viewing at mvbookfestival.com. The next discussion is an Evening With the Supreme Court featuring authors Adam Cohen, Richard Lazarus and Ruth Marcus, and moderated by Dahlia Lithwick. It takes place on August 9 at 7:30 p.m.