James Dayton, principal of the Minneapolis architecture firm James Dayton Design, once described the buildings he designed as “large-scale sculptures,” with expressive forms and unexpected materials that charmed their inhabitants and delighted passersby.

He died unexpectedly on Tuesday at age 53; the cause of death was not immediately known.

Dayton was among the Twin Cities’ most sought-after architects and received the American Institute of Architects Young Architect Award in 2006. His firm’s best-known local projects include the MacPhail Center for Music in Minneapolis’ Mill District, the Minnetonka Center for the Arts, and, most recently, an ebullient, modern addition to the historic Westminster Presbyterian Church on Nicollet Mall.

Dayton’s design career began with window displays he created for his family’s department store back in high school (founder George Draper Dayton was his great-great grandfather).

After receiving bachelor’s and master’s degrees in architecture, from Yale University and University of Virginia, respectively, Dayton spent five years working for internationally renowned architect Frank Gehry in Santa Monica. He was involved with several of Gehry’s iconic projects, including the Guggenheim Museum in Bilbao, Spain, and the Walt Disney Concert Hall in Los Angeles.

Dayton returned to Minnesota and launched his namesake firm in 1997, designing projects ranging from private homes to campuses of the Blake School.

Whether working in copper, weathering steel, glass, wood or zinc, Dayton developed a reputation for designing buildings that felt both fresh and timeless, creating spaces filled with light and whimsical details.

“Jim had a remarkable ability to do cutting-edge design, often with daring forms and unusual materials, in ways that also fit their surroundings and respected their context,” said Tom Fisher, a University of Minnesota professor and director of the Minnesota Design Center.

MacPhail, Fisher said, has “energetic building forms that tilt in and out, as if they are dancing to the music inside, and rusted-steel cladding the color of a fine, stringed instrument.”

Timothy Hart-Andersen, senior pastor at Westminster, said that the addition Dayton designed captured what the congregation is trying to do theologically — be engaged with the city, highly accessible and sustainable. He described Dayton as gracious and down-to-earth and said he was remarkably patient throughout the six-year project.

His firm also designed several notable Minneapolis residential buildings, including the Bookmen Lofts and Bookmen Stacks, as well as restaurants such as the Bachelor Farmer and Restaurant Alma.

Dayton’s design abilities even extended to a wingtip dress boot he created for the Allen Edmonds shoe company following a commission to design its City Center store.

Eric Dayton, whose father, former Gov. Mark Dayton, is the cousin of James’ late father, Robert Dayton, reflected on the “bright light” lost by the family and community.

“I grew up admiring Jim as an older cousin,” Eric Dayton said in an e-mail. “Over time, I came to know him as a great friend, a gifted architect, and a wonderful partner on a number of projects. It’s hard to believe that he’s gone, but I feel grateful for the time I spent with Jim and we’re all fortunate to be able to experience the beautiful public spaces he created for many years to come.”

This fall, Westminster plans to realize Dayton’s final vision for the church by completing its bell tower, so its daily ringing may become yet another of the small glories of urban life, much like Dayton’s architecture.