Mexican architect Carlos Garciavelez and New York designer David Lawrence share a Lhasa Apso named Lolo, a background in luxury fashion, and a knack for creating unexpected and opulent spaces. And although they soft-launched their New York–based design firm, Carlos David , three years ago, the couple managed to keep most of their projects under wraps—that is until now.

“I think it’s really important to do the work first and then show people,” says Lawrence, who’s been creating high-end residential and commercial interiors for more than 15 years, following an early career in fashion merchandising with Giorgio Armani . It’s a sentiment shared by wunderkind architect Garciavelez, who was only 28 when he was invited to join the faculty of the Harvard Graduate School of Design , after receiving the prestigious Druker Fellowship and the Urban Planning and Design Thesis Prize from the university. He, too, boasts an impressive fashion résumé, including a stint at Alexander McQueen’s design studio in London and the launch of his own menswear label, which earned him GQ’s Emerging Designer of the Year prize in 2017.

Hand-painted de Gournay wallpaper blossoms in the dining room, where gilded birds and frogs perch in the branches of a pair of Paula Swinnen candelabra. The designers recruited a pair of 1950s Maison Jansen writing tables to serve as dining tables, which can be pushed together for grand affairs or apart for intimate suppers. While the rest of the room shimmers in gloss and gold leaf, the floor is grounded with a more casual rug by Doris Leslie Blau , an homage to Swedish midcentury designer Märta Måås Fjetterström. “It’s a little muted and very unexpected,” says architect Carlos Garciavelez, noting that the choice keeps the decadent room from slipping into fussy territory.

“I was more on the business side of fashion,” Lawrence explains, “so whereas I’m more pragmatic, Carlos is very…”

“Experimental!” Garciavelez jumps in with a laugh. “It’s good: He grounds things, he’s able to edit, and I’m able to explore.”

The duo have been doing plenty of exploring of late, with a wildly diverse portfolio of projects, from an ultramodern glass pavilion in Barcelona to a classic art-filled Fifth Avenue piede-à-terre and a tailored Upper West Side apartment in Manhattan. Most recently, they completed an extensive renovation and redesign of a six-floor, five-bedroom Upper East Side townhouse owned by notable art collector and philanthropist Nancy McCormick, a longtime Lawrence client who’s an American Ballet Theatre trustee and founder of the children’s clothing line Florence Fancy .

The walls of the show-stopping primary bath are clad in custom blue quartzite panels, inspired by the Frick Collection’s garden courtyard. “The material is just extraordinary,” says designer David Lawrence. “It has texture and depth, and it twinkles almost like a piece of jewelry—the entire wall is like a gem.” Fabrication of the semi-precious stone (which owner Nancy McCormick selected from ABC Worldwide Stone in her favorite shade, blue) demanded absolute precision. “It essentially disintegrates when you try to cut it,” says Garciavelez. “But it gives the house a very strong and very feminine character.”

“She’s someone who wants things to be very, very sophisticated and elegant,” Lawrence says of the vivacious mother of three. “It doesn’t look like a super-casual, of-the-moment home—this is definitely more classic and grown-up.” The pair focused on seamlessly integrating McCormick’s art collection and inherited furniture (she’s a descendent of William Deering and of Cyrus McCormick, who invented the mechanical reaper and revolutionized modern farming), with new acquisitions and their own bespoke creations.

They gut-renovated McCormick’s fifth-floor primary suite down to the studs, moving the bedroom to the south side of the 18-foot-wide home, cloaking the bathroom in blue-quartzite panels inspired by the garden court of the Frick Collection , and devising a show-stopping dressing room—complete with a gleaming silver leaf ceiling. The stairways and corridors of the 8,500-square-foot home were changed from a “margarine yellow” to a glamorously lacquered black–and–pearl white, a nod to Coco Chanel’s original Parisian store. Garciavelez and Lawrence reimagined the dining room as a gilded forest, papering the walls with de Gournay’s handmade chinoiserie blossoms and nesting treelike candelabra atop two 1950s Maison Jansen writing desks, cleverly repurposed as dining tables. “They just fit the bill in the most magical way,” says Lawrence, explaining that the desks can be separated for intimate supping or pressed together for grand entertaining—a moveable feast.

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The living room, meanwhile, became a home gallery, displaying McCormick’s impressive art holdings (including an 1876 John Singer Sargent portrait of her great-great-grandfather Charles Deering, previously on display at The Art Institute of Chicago ) above an amorphous travertine-and-bronze Franck Evennou table and a curving royal blue sofa, designed by Carlos David in decadent silk velvet and leather.

“You have that juxtaposition—it’s unexpected,” notes Garciavelez. “The table is a classic purchased piece, and the sofa is designed by us, but there’s this sense of communication between them.” As Lawrence summarizes, “Every decision, crevice, corner, nuance, moment is 1,000% considered.”

Including the sixth-floor terrace (designed by Harrison Green ), where last July, after completing the renovations, the couple got engaged. “It sounds a little hippy-dippy,” says Lawrence, “but I really think so much of what goes into our work—and the ultimate outcome—is a product of joy and, to some extent, love.”

“How do you create the perfect princess room for a 10-year-old?” Lawrence asks. “A pink-and-gray canopy bed and an over-the-top print on the blankets and pillows,” Garciavalez answers. The ferocious tiger-striped throw and pillows are by Saved NY —in 100% cashmere, naturally.