The AD100 designer's Bed-Stuy rental is a seductive laboratory for his own finely crafted creations

Mark Grattan (wearing a Loro Piana top and pants, Celine shoes, Tom Ford glasses, and Versace necklace) in the living room of his Brooklyn apartment. Fashion styling by Tiffani Williams. Florals by Olivee Floral.

It's a sunny, unseasonably warm morning in early March and Amiga, Mark Grattan ’s Himalayan cat, is vibing. One moment, she’s splayed across the marquetry top of the dining table. Another, she’s nuzzling against the plush pile of a moiré-patterned rug or bounding across the platform bed, the lacquered frame of which appears to melt into the floor. “It’s her apartment,” Grattan says. True. But it’s his world. On the top floor of a Brooklyn brownstone , the AD100 iconoclast has realized an immersive feat of contemporary design—and by hand no less.

He wasn’t expecting to live here.…