Apr 6, 2015 12:11 PM

Vincent Lardo owes it all—his six New York Times bestsellers, a three-decade career and a crossroads that may have never been—to the invention of one machine.

“I was working in the advertising field for Burson-Marsteller, which did public relations for the industry giant Young & Rubicam,” the 84-year-old Amagansett resident recently recalled. “In the mid-1980s, the word processors arrived. After learning to use one, I gave up the usual two-martini lunch, would close my office door and spend my lunch hour writing.”

His first effort—a “mainstream” mystery, he said—was rejected by every publisher he sent it to. But that wasn’t enough to dissuade him.

“As a gay man, I wondered what would happen if I changed the story to appeal to that market,” he said. “I went back to the word processor, killed the protagonist’s wife, and gave him a gay son. Voila! I had an offer from Alyson Publications.”

“China House” was published in 1983. He was 52 years old, a man whose childhood began in the Bronx, where he attended the former Evander Childs High School, followed by the City College of New York. With the Korean War raging, he enlisted in the Army in 1952.

“In July of ’53, I’m on a troop ship in Seattle, about to sail to Korea. But we never left the dock,” he said. “The armistice ending the war was signed the same day we were scheduled to leave.”

The next year he spent stationed in Japan and, upon his discharge in 1954, Mr. Lardo enrolled at Fairleigh Dickinson University in New Jersey under the G.I. Bill, earning a degree in English literature. An entrèe into the banking industry led him to Madison Avenue. In 1998, he retired and moved from Manhattan to his second home in Amagansett with his partner, Bob Evans, who died a year later.

Ensconced on the East End, Mr. Lardo began work on another attempt to break into the mainstream literary market with a mystery set in the Hamptons. His effort was rewarded in 1999, when Putnam Press published “The Hamptons Affair.”

But while working on its sequel, “The Hampton Connection,” Mr. Lardo was offered a life-changing opportunity: Renowned author Lawrence Sanders—who had penned the hugely popular “The Anderson Tapes,” “Deadly Sins” and “Archy McNally” series—had died in 1998, and Mr. Lardo’s agent called to ask, “Would you like to take over the McNally series?”

“I knew, of course, who Sanders was. His ‘Deadly Sins’ novels were brilliant, some of my favorites, but I was not familiar with Archy McNally and had some hesitation on accepting the offer,” Mr. Lardo said. “I told my agent, ‘Having never read one, I don’t know if I can write one.’”

The next thing he knew, the seven existing McNally books arrived at Mr. Lardo’s door. After reading the first in the series, “McNally’s Secret,” he was pleased to find that Archy McNally had a lot in common with his “Hamptons” character, Michael Anthony Reo. “Both lived in upscale resort towns—McNally in Palm Beach; Reo, East Hampton,” he said. “Both moved among the rich and famous, enjoyed wine, women and song. They both lived a stone’s throw from the same ocean, separated by a mere 1,200 miles. I felt like I knew Archy.”

Archy’s fans agreed, placing all six of Mr. Lardo’s McNally novels on The New York Times bestseller list. In fact, the takeover was so smooth that a Publishers Weekly reviewer missed the switch.

By 2013, Mr. Lardo had returned to familiar territory—the gay/lesbian genre—with “The Jockstrap Murders.” And now he is back in unchartered waters.

“I’m working on a young adult historical novel I call ‘The Last Alexander,’” he said. “It tells the story of Alexander Helios, the son of Cleopatra and Mark Anthony, who is captured and taken prisoner by Octavian Caesar.”

When asked why he would look to break into a new genre after the success he’s had with his gay and mainstream novels, Mr. Lardo smiled. “I’d love to get a movie deal from one of my books. The YA’s are hot right now,” he said, referring to the burgeoning genre of young adult literature. “Look at the phenomenal popularity of the ‘Harry Potter’ and ‘Twilight’ series. Young people are reading the books and going to the movies. As a writer, that’s a great thing to see.”

The follow-up question, “Why did you choose to write a novel set 2,000 years in the past?” drew a laugh from the author.

“Well, obviously, at my age, I couldn’t write about what kids are doing today. I have no idea,” he said. “But I’m a history buff and know I can tell an entertaining yarn based on the life of Alexander Helios. And the timing is great. ‘Game of Thrones’ has whet people’s appetite for the mystery and adventure found in ancient times.”

With the fifth season of the HBO epic drama—based on George R.R. Martin’s best-selling eponymous book series—premiering on Sunday, April 12, Mr. Lardo is determined to finish “The Last Alexander” this summer.

“A novel is a novel. I’m trying to keep true to the historical record, but my number-one goal as an author is to keep the reader entertained and turning the pages,” he said. “That’s my task for this book, as it was for everything I’ve ever written.”

Mr. Lardo has been up to that task for more than 30 years. At age 84, he continues to craft books that will be published, much as he did when he started in the 1980s, with one small difference: He now works on a laptop computer.

The word processor went into the trash with his eight-track tape player.

For more information on Vincent Lardo, visit vincentlardo.com.