Gary Regan, a British-born bartender who helped propel the “craft cocktail” movement of the past quarter century with his convivial and densely researched “The Joy of Mixology” and other books and articles about liquors, mixed drinks and life behind the bar, died Nov. 15 at a hospital in Newburgh, N.Y. He was 68.

He had pneumonia and complications from cancer, his wife, Amy Gallagher, announced on social media platforms.

Mr. Regan grew up working in his family’s pubs in Lancashire, England, before coming to the United States in the early 1970s. While tending bar in New York City, he cultivated a reputation as both a clever raconteur and a skilled master of the cocktail.

“Drinks are not the main reason to tend bar,” he told Drink magazine in 2018. “The most important thing a bartender can do is make people smile.”

He began writing for FoodArts magazine in the early 1990s — describing himself as “a bartender with a writing problem” — and published his first of 18 books, “The Bartender’s Bible,” in 1991. He later became a cocktail columnist for Wine Enthusiast, Food & Wine and the San Francisco Chronicle.

“Gary was one of the first people to take a more modern and scholarly-based approach to what we drink and why,” Noah Rothbaum, a writer and co-host of the podcast “Life Behind Bars,” said in an interview. “His goal was to make the world drink better.”

In 1995, with his then-wife, Mardee Haidin Regan, Mr. Regan published “The Book of Bourbon and Other Fine American Whiskeys,” which delved into the cultural origins and distilling methods of bourbon and became “one of the foundational texts of the cocktail revolution,” David Wondrich, a writer and historian of cocktails, said in an interview.

The couple’s 1997 book, “The Martini Companion,” explored the enduring mystique and appeal of perhaps the most storied cocktail of all.

“In order to make a first-rate Martini,” they wrote, “you must do so lovingly; you must show a little respect for the drink. Stirring a Martini is a contemplative exercise that requires great concentration.”

With “The Joy of Mixology” (2003), Mr. Regan composed a guide to cocktails that was every bit as comprehensive and influential as Irma S. Rombauer’s “Joy of Cooking.”

“His book was really an attempt to put everything in one place: Here’s the complete guide to the art,” Wondrich said. “It’s a magnificent book, and, at the time, it was revolutionary.”

“The Joy of Mixology” sought to raise the job of bartending to a profession built on time-honored standards. The book became a guidepost for the craft cocktail movement that emerged across the country and throughout the world.

In “The Joy of Mixology,” Mr. Regan explored the history of mixed drinks, described the equipment and skills needed to work behind a bar and showed that hundreds of cocktails are variations on a few basic recipes and techniques.

“His easy-to-read style demystified drinks-making for the home (and pro) bartender,” Washington-based cocktail author Philip Greene wrote in an email, “and his ordering of cocktails into various categories made it all that much more accessible.”

At a deeper level, beyond detailing the shakers, strainers, glassware and garnishes needed to prepare drinks, Mr. Regan examined the philosophical and ethical questions underlying the bartender’s craft.

He wrote of alcoholism as a chronic hazard of the profession and of the bartender’s need to be prepared for belligerent customers: “Whatever the situation, even if it means losing face, you should always try to pacify, not further anger an upset customer.”

Bartenders should be friendly and attentive, but should maintain a certain emotional distance: “Wear a wedding band at all times — whether you’re married or single.”

Near his home in Cornwall-on-Hudson, N.Y., Mr. Regan led two-day seminars dubbed “Cocktails in the Country,” which became hugely popular among cocktail aficionados and aspiring bartenders. In his workshops and speeches, he emphasized “mindfulness,” meditation and an easygoing approach to working behind the bar.

“If you make your customers feel good, they’ll never forget you,” he said at the 2016 Tales of the Cocktail conference in New Orleans. “Make one guest happier when he or she leaves your bar than they were when they walked in, and you’ve changed the world.”

Gary Lee Regan was born Sept. 18, 1951, in Rochdale, near Manchester, England. He began working in his parents’ pub at 14, then left school a year later.

He moved to New York at 22, when his first marriage broke up. He spent four years as the manager of the North Star, a British pub at the South Street Seaport, where he became renowned for his knowledge of obscure whiskies, his bushy beard and his comical stories.

He often made syrups, fruit juices and other ingredients for his bar, then later marketed a brand of bitters under his own name.

During the 1980s, Mr. Regan was, in his words, “a total drunk,” but he managed to moderate his drinking habits without quitting altogether.

“My ‘coming out’ on this issue is a way of opening a conversation that needs to be started in the bartending community,” he told Difford’s Guide, an online cocktail forum, in 2011. “Bartenders have always drunk a lot, and it’s important we talk about it.”

In 2003, Mr. Regan underwent surgery and radiation treatment for cancer of the tongue. No longer able to grow a full beard, he began wearing his hair long and adopted the Lancashire nickname for Gary, “Gaz.”

He sometimes wore eyeliner under one eye, as “my latest affectation” and as a reminder for bartenders to look their customers in the eye.

His second marriage, to Mardee Haidin Regan, ended in divorce. Survivors include Gallagher, his wife of 11 years.

Mr. Regan won numerous awards for his cocktail writing, worked as a consultant with liquor companies and traveled the globe as a speaker and judge of cocktail contests. In 2018, he published a revised edition of “The Joy of Mixology.”

If he had a signature cocktail, it was the negroni, made with gin, Campari, sweet vermouth, a twist of orange peel — and a special twist of his own.

“Just for a bit of fun, I started stirring them with my finger and everyone laughed,” Mr. Regan said in 2014. “It’s just something that carried on. It took me a while to understand why it was a good idea — it’s because it puts a smile on everybody’s face.”