The Footwear News Achievement Awards, sometimes called the Oscars of shoes, shines a spotlight on the industry’s top designers. But when the singer Dua Lipa won for a Puma collection last November, her frequent collaborator Billy Walsh bolted at the sight of flashing cameras.“Billy Walsh’s five-seconds limit on the red carpet,” Ms. Lipa said, as photographers shouted her name at Cipriani Wall Street.“More like two seconds,” Mr. Walsh, 40, added safely from the sidelines.Avoiding attention is a peculiar trait for a man who collaborates with some of the biggest names in pop, including Ms. Lipa, Post Malone and the Weeknd, straddling the upper echelons of fashion and music.He has collaborated with Rihanna on a Fenty collection with Puma, and consulted Kanye West on video directors. As a fashion stylist, he dressed the Weeknd in Givenchy for the Met gala and James Blake in Yohji Yamamoto for awards shows.But his biggest achievements are in songwriting. His co-writing credits include “Sunflower” by Post Malone and Swae Lee, and six tracks on Mr. West’s “Donda” album — and those are just counting his Grammy nominations.“Billy is part of a small group of people in this industry that I consider to be like family,” Mr. Malone said by email. Their shared writing catalog also includes the hits “I Fall Apart,” “Better Now,” “Wow” and “Circles.” “Not only is he one of the best songwriters, but he is a brilliant creative and fashion designer.”Dua Lipa and Mr. Walsh won collection of the year award at the Footwear News Achievement Awards last November.Evan Agostini/Invision, via Associated PressMr. Walsh has written numerous songs for Post Malone, seen here at a Spotify concert in 2022.Antony Jones/Getty ImagesOn a recent Tuesday afternoon, Mr. Walsh went shopping at Dover Street Market, the retail temple in Manhattan where he often goes for inspiration. “I would come here to do massive pulls for the Weeknd,” he said. “I used to start on the top floor and work my way down.”He still does. As he flipped through racks of Raf Simons and Junya Watanabe on the seventh floor, Mr. Walsh recounted this unorthodox rise in the recording and street wear industries. “Fashion and music are definitely interrelated, but I guess I don’t know too many people who have succeeded in both,” he said. “I stay in the back and don’t need credit.”Dressed in an all-black “uniform” (T-shirt, Prada nylon shorts, Alyx socks and Nike Air Tuned Max sneakers), with his signature shaved head and chrome-metal grills, he has the tough-guy appearance of a post-apocalyptic British rude boy.Mr. Walsh credits his dexterity to his rough-and-tumble upbringing in the Jamaica Plain neighborhood of Boston. His father, William Walsh, a folk musician who performed at local Irish pubs, encouraged him to write poetry and dance. He was also an obsessive sneaker head. “I drove my mom crazy looking all over the city for the Adidas Equipment Basketball shoes with the interchangeable, different-colored socks,” he said.Other addictions followed. He started drinking at 11, often getting into after-school brawls until he sobered up a decade later.Mr. Walsh at his home in Los Angeles.Jack Bool for The New York TimesAt 18, he headed to Los Angeles to study dance at Loyola Marymount University, and signed with an agent. But dance gigs were few and far between, so he spent most of his 20s as a nightclub promoter, working alongside his brother at Hollywood hot spots like Emerson Theater and Hyde, where he would party with a young Post Malone and future designers like Matthew M. Williams of Givenchy.In 2011, the choreographer Fatima Robinson, who he met at Eden, a Hollywood nightclub, encouraged him to stop dancing and focus on poetry and design instead. “This woman literally saved my life,” he said.He quit auditioning and busied himself with writing poetry and daydreaming about street wear. He looked inside his sneaker closet and began experimenting with Frankenstein combinations. One of the first designs cobbled together was a white Nike Air Force One with a black rubber creeper sole. “I always wondered what a creeper would look like with certain old sneakers from my childhood,” he said.He wore his custom sneakers to the clubs, which would get noticed by emerging V.I.P.s like Virgil Abloh and Travis Scott. In 2014, with seed money from fellow party promoters, he and a friend started a street wear label called Mr. Completely, which reimagined classic sneakers including Adidas Sambas and Stan Smiths.Mr. Walsh added a creeper sole to an Adidas Stand Smith for his streetwear brand, Mr. Completely.via Billy WalshTo promote the brand, he held a party at Fourtwofour on Fairfax and invited everyone he knew. Among them was the stylist Jahleel Weaver, who ordered several pairs for his client Rihanna. That turned out to be a propitious sale. A few months later, Rihanna invited Mr. Walsh to design her debut collection with Puma (which went on to win the Footwear News “Shoe of the Year” two years later).Sneakers opened other doors. One of them led to Illangelo, a veteran Canadian producer, who became a confidant and his unexpected entree into music writing. Once again, it started at a nightclub. The two were clubbing on the Sunset Strip in 2014 when Illangelo mentioned that he needed a new songwriter. Seizing the moment, Mr. Walsh shared a short poem from his iPhone Notes app.Illangelo was so impressed that he brought Mr. Walsh into studio sessions with Alicia Keys and he ended up getting his first mainstream writing credit on the song, “In Common.” Illangelo also introduced Mr. Walsh to the Weeknd, who at first was only interested in working with him as a stylist. (The two shared an appreciation for military bomber jackets.) But as Mr. Walsh’s reputation as a songwriter began to rise, the Weeknd began bringing him into the studio.Mr. Walsh dressed the Weeknd for the Met Gala in 2016.George Pimentel/WireImageMr. Walsh dressed James Blake in Yohji Yamamoto for the Grammy Awards in 2020.Frazer Harrison/Getty ImagesThose sessions resulted in three tracks from the 2016 album “Starboy,” including “True Colors” and “Die for You,” which peaked at No. 6 on the Billboard Hot 100 this month, seven years after it was first released, thanks to going viral on TikTok.Mr. Walsh has since gone on to write more than 100 songs for artists as varied as the Kid Laroi (“Without You”), pop powerhouses like Mr. Malone and Ms. Lipa, and rock royalty like Ozzy Osbourne (“Ordinary Man”). His publishing catalog has racked up a combined 20 billion streams. Last November, “Sunflower” went 17 times platinum, becoming the highest-certified single of all time.His soaring music career hasn’t stopped him from other creative pursuits. In 2016, he started Donavan’s Yard, a nightlife collective in Los Angeles with the D.J.s Drew Byrd and Sean G that hosts parties in Tokyo and a streaming concert series on Amazon Music Live. Branded merch is sold at Dover Street Market,In October, he started a conceptual street wear label called Iswas with Keith Richardson, his creative partner at Mr. Completely. The label currently sells one item: a pair of painter’s pants made from Japanese selvage denim that costs $450.Despite his many accolades, Mr. Walsh prefers being behind the scenes. “I am never the main focus, just as it should be,” he said. Jack Bool for The New York TimesWearing many hats, Mr. Walsh said, affords him creative freedom. “If Abel knows I am winning an award with Dua and doing my own clothing line, he respects that I’m doing OK for myself,” he said, referring to the Weeknd by his given name. “No one feels like you’re too dependent.”Back at Dover Street, Mr. Walsh went from floor to floor, examining the clothing racks like an archaeologist at a fresh dig. On the shoe floor, he picked up a pair of cloven-toed “tabi” boots by Martin Margiela. “I appreciate what this guy does,” he said of the designer, who, like himself, shuns the limelight in favor of letting his work speak for itself.After about two hours, he reached the Rose Bakery on the ground floor, took a seat and ordered an Earl Grey tea. As ambient music played overhead, he reflected on his unusual journey. “My success comes from artists recognizing that I see the creative process as sacred, somewhat secret,” he said. “I am never the main focus, just as it should be.” More