A sprinkling of tiny tattoos covers Christian Cowan’s fingers and arms: a pale stag, a walrus, a sewing needle and the word “intimacy,” so faintly scrawled that it is barely legible.

That fine ink is a tell.

“I’m an introvert,” Mr. Cowan said over lunch of vegetarian rigatoni at Sant Ambroeus in Greenwich Village last month. “I vent any need to be out in the limelight through my work.”

His work is as raucous as his ink is discreet. Mr. Cowan, 28, a Londoner settled in New York City, made his name by confecting the vibrantly colorful sequined and feathered club wear that is catnip to the party crowd, to say nothing of the effusively spangled performance gear he has whipped up for high-wattage celebrities including Lady Gaga, Cardi B and Lil Nas X.

These days, he is also linked with the pop star Sam Smith, a fellow Brit. Their frequent outings have given rise to speculation that they are an item.

They appeared together at the White House in December, witnesses to the signing of the Respect for Marriage Act. They have been photographed strolling Manhattan arm in arm. On one occasion, Smith was snapped planting a kiss on Mr. Cowan’s temple; on another, greeting the designer’s parents outside a West Village restaurant.

More recently the singer, who uses they/them pronouns, wore a custom Christian Cowan green pheasant-feathered cape and ostrich headpiece for the steamily provocative music video for “I’m Not Here to Make Friends” — one of the pair’s several collaborations.

And on Valentine’s Day, Smith was seated in the front row for Mr. Cowan’s fall 2023 fashion show in New York City. They wore full Cowan regalia: a flame red jumpsuit and dazzling silver coat, an unabashed homage to the designer’s over-the-top aesthetic.

Given all that exposure, some may find it perplexing that Mr. Cowan is tight-lipped about the relationship, with talk of his private life strictly off limits. “My work has become so all-consuming that I try to reserve parts that are just for me,” he said.

His silence seems coy, especially since he did not deny rampant media speculation about his romance with the star.

He maintains that when he isn’t in his SoHo studio, he leads a cloistered life, listening to jazz, watching television documentaries and “seeing what the James Webb Space Telescope is up to,” he said.

He plans to put down roots in the West Village. “I love it here,” he added. “I absolutely want to get married and have kids here — the whole shebang.”

Mr. Cowan’s vision of settled domesticity might seem markedly at odds with the flamboyance of his collections. Not at all, he would argue. His cozy fantasy is but one expression of the protective shell he developed as a boy.

“I went to a very sporty, conservative school,” said Mr. Cowan, who grew up near Cambridge in the British countryside, the son of scientists. “In the country, I was isolated, bullied — a very unhappy teenager. Growing up gay, I struggled with all the worst issues.”

He found a kind of spiritual kinship in the designs of Alexander McQueen, which often made reference to insects and butterflies. “Growing up, I wanted to be an entomologist,” Mr. Cowan said. “I soon realized that you could create your own insects through fashion.”

His preoccupation with six-legged creatures extends to his private life. At home in Greenwich Village, “I have hundreds of insects in frames,” he said. “The place looks like Indiana Jones’s apartment.”

He was no less entranced in his youth with “Sex and the City.” “If I’m honest, the show provided a much-needed glimpse into a future that I could have, the idea of this world where fashion was paramount, where everyone could be who they wanted to be and everything was fabulous,” he said. “The complete freedom of the metropolis, that was for me.”

Pop stars inspired his first raw attempts at fashion. “I was a kid making outfits on my bedroom floor,” he said. “I super-glued them together. They were atrocious, but I’ve got them all stored in my mother’s attic.”

At 14 — “my peak sad time,” he called it — he fell in love with Lady Gaga’s music. Later, during his first year at Central Saint Martins, the prestigious art and design school in London, he gave a mini-presentation of outfits inspired by his idol. “Then, by some strange turn of events — I never knew exactly which — Gaga saw them online and wore them,” he said.

He was shaken. “There was my idol, wearing my clothes,” he said. That early taste of success, and an infatuation with Manhattan he had nurtured since he was 10, emboldened him to decamp for New York.

On arriving in 2017, “I had no plan,” he said. But Manhattan suited him as the ideal place to cultivate and promote the label he had founded a year earlier. “I wanted to be here, to be this brand that Upper East Siders feel fabulous wearing, as much as Lower East Side club kids.” (Note: Few club kids are likely to spring for clothes that vary in price from about $600 for a zebra-print halter dress to $10,000 for a black-and-white feather coat.)

Word of his talent reached Anna Wintour, who, while vetting candidates for the 2018 CFDA/Vogue Fashion Fund, trekked up four flights of stairs to his studio at Lexington Avenue and 30th Street. She liked what she saw. “She put me in the fund that year,” Mr. Cowan said.

He has rarely looked back.

Just over a year ago, Mr. Cowan opened his first store, on Wooster Street in SoHo, as a temporary showcase for his extravagant designs, its powder pink interior flirting with camp without forfeiting a sense of opulence. The store, now closed, provided a template for future ventures.

He will most likely follow up next year with a shop in Las Vegas, which he described as “a part of America that I’m obsessed with”: “Everyone is drinking, people have money and they’re shopping so late, giving in to frivolity and fabulousness.”

The store would be appropriately flashy, he added. “We may do it all in silver.”

Adventurous to the bone, Mr. Cowan planned to fly to London the next morning to discuss designing costumes for a Broadway show, which he said contractual obligations prevented him from naming. “I’ve been desperate to do costume design in addition to my brand,” he said. “It gives me a completely different brief to sink my teeth into.”

His latest show signaled a noteworthy shift in direction. “My past collections were full of bombast — loud and intense,” Mr. Cowan said. This time he was inspired by Judy Garland and, in particular, a melancholy recording of one of her last concerts. In keeping with its somber mood, the models walked in tailored suits, ultra-spare gowns and, in one memorable instance, a shroud-like, feather-trimmed sheer black veil.

“The show was imbued with a sense of mortality,” Mr. Cowan said. “As I’ve grown up, I’ve addressed sadder topics, deeper themes.”

All was not doomy. There were cerulean silk dresses edged in feathers, fan-like plumed headdresses and a lavishly feathered cape coat that ended the show on a frankly extravagant note.

“I will always continue with my feathers and crystals,” Mr. Cowan said. “Those are the paints that I’ve chosen.”