Hugh Newell Jacobsen, an award-winning Washington architect whose deceptively simple designs for homes and prominent public buildings honored the values of traditional styles while cleverly infusing modernist sensibilities, died March 4 at an assisted-living center in Front Royal, Va. He was 91.

The cause was complications from covid-19, said his son John Jacobsen. Another son, Simon Jacobsen, said the cause was reoccurring pneumonia and unrelated to the coronavirus.

Throughout a career that included high-profile commissions around the world, Mr. Jacobsen was best known for residential designs that combined the familiar forms of early American architecture with modern architecture’s emphasis on simplicity and clean lines.

Mr. Jacobsen’s hallmark was often described as a Monopoly house because of its resemblance to the piece from the board game. The light, airy, steeply gabled pavilions were not nearly as easy to create as they might have appeared. “Designing is like giving birth to a barbed wire fence,” he often quipped.

He won some of his profession’s highest accolades, Architectural Digest inducted him into its hall of fame, and he was a regular member of the AD100, the magazine’s annual list of the world’s top architects and designers.

With a rakish sweep of white hair, impeccably tailored suits and patrician bearing, Mr. Jacobsen moved easily among such wealthy clients as former first lady Jacqueline Kennedy Onassis, actors Meryl Streep and James Garner, and arts patron and philanthropist Rachel “Bunny” Mellon.

Mr. Jacobsen, who had been mentored by modernist masters Louis Kahn and Philip Johnson, began applying their philosophies about order and clarity as soon as he opened his solo architecture practice in Washington in 1958. In time, more than 120 houses in the Georgetown neighborhood were refurbished or built by him.

He also undertook major public projects. He created the addition under the West Terrace of the U.S. Capitol, restored two Smithsonian museums — the Renwick Gallery and the Arts and Industries Building — and renovated the Talleyrand building, part of the U.S. Embassy complex in Paris, and the Spaso House, the U.S. ambassador’s residence in Moscow. He designed buildings at the University of Michigan, the University of Oklahoma, Georgetown University and his undergraduate alma mater, the University of Maryland.

Mr. Jacobsen’s reputation flourished in the 1980s after Onassis hired him to design her home on Martha’s Vineyard, Mass. Built in 1981, Red Gate Farm caused an uproar in the island community because of fears his modern design would look out of place among the surrounding picturesque cottages.

But the understated house was more New England saltbox than brutalist concrete fantasy. In describing his visit to the house, author Robert T. Littell wrote, “There was something about the inside of both [the main and guest] houses that made you feel you were being wrapped in a big robe of clean, soft, white terry cloth.”

In his best-remembered residential projects, Mr. Jacobsen’s trademark became a series of steep-roofed pavilions unfurling like a telescope. His houses had elongated windows to draw natural light into the space and pervasive white walls to reflect it throughout the room.

“If there is anything that is consistent in my work, it is my absolute obsession with controlling light,” he once told the Washington Star. “I have found that I can hold light in a space almost as you can fill up a glass with liquid.”

Hewing to the modern aesthetic, Mr. Jacobsen’s homes lacked ornamentation — no molding, baseboards or trim. Canister lights were a consistent motif. Bookshelves were designed on a grid to resemble antique wooden egg crates.

Often copied, Mr. Jacobsen’s bookshelves were precisely crafted to be elegant as well as functional. Each cube was 12 inches wide so books could be removed without starting an avalanche. Filling the shelves with a library turned them into a wall of color. (Don’t leave them empty, the architect begged, or “they’ll look like a liquor store going out of business.”)

In 1998, Mr. Jacobsen was one of the few architects selected to participate in Life magazine’s Dream House series. The editors commissioned architects to design beautiful yet affordable houses for aspiring middle-class homeowners. The mail-order home plans sold for about $600 for a house with a projected construction cost of $200,000.

More than 900,000 Jacobsen plans sold, and houses created from the plans were built from South Korea to the United Kingdom to Argentina.

“I’ve been an architect for the rich, I’ve been a ‘Jackie-tect’ — that’s what one of my sons has called me since I did Mrs. Onassis’s Martha’s Vineyard house — but to do a house that people can reasonably build, that’s how every architect wants to be remembered,” Mr. Jacobsen told Life.

Hugh Newell Jacobsen was born in Grand Rapids, Mich., on March 11, 1929, and spent his early years in what he termed a “Coca-Cola Colonial,” a cookie-cutter version of the real thing. His father, a meat importer, became an official with the War Shipping Administration during World War II and relocated the family to Washington.

After graduating in 1947 from the District’s Wilson High School, Mr. Jacobsen received a bachelor’s degree in fine arts from U-Md. in 1951. He wanted to become a portrait painter, but his father suggested architecture as a more secure field. He overcame his dyslexia to receive a master’s degree in architecture from Yale in 1955.

Mr. Jacobsen joined Johnson in his Connecticut office immediately after graduation but was fired within a year because of his poor skills as a draftsman. After two years in the Air Force, he returned to Washington and “took pleasure in being fired a few more times by some of the city’s more unprogressive firms,” he recounted in an interview with Architectural Digest, before starting his own company.

His wife of 58 years, the former Ruth “Robin” Kearney, died in 2010. Survivors include three sons, John of Bellevue, Wash., Simon of Delaplane, Va., and Matthew Jacobsen of West Hollywood, Calif.; and seven grandchildren.

Hugh Newell Jacobsen’s work could be difficult to characterize and often left critics floundering for shorthand descriptions. Some called him a “classical modernist,” a label that Mr. Jacobsen disdained because he felt it was derogatory. He once joked to The Washington Post that it was “a little bit like saying you have the clap.”

His designs were almost the opposite of his blunt, exuberant personality, seeking the essence of the regional vernacular in a modest, respectful form. They were subtle suggestions rather than boisterous commands.

“Good architecture never shouts,” Mr. Jacobsen told the Star. “It is like a well-mannered lady, kind to its neighbors. It takes a double take to know that she is there at all.”