“It was an emotional reaction,” says Hillary Clinton of her first visit to what is now her Beltway home, dubbed “Whitehaven” because it’s nestled on Whitehaven Street in the tony Massachusetts Avenue neighborhood of Washington, D.C. “When I was elected to the Senate in 2000, I knew that I needed a place to live while we were in session during the year. So I began looking. And, I had an experience in this house, which was just emotional. I had gone up to the third floor and looked out over the trees—to the back of the British embassy—and I just felt like I was in old-time London or New York. The gardens were just the most amazing that I had seen anywhere in my real-estate tour,” she says.

While the attraction may have been love at first sight, the Clintons also knew that the home—a Neo-Georgian red-brick 5,500-square-foot house that had been built in 1951—would nonetheless require extensive renovations. “The mandate was to bring more light and to create more physical space for sitting and relaxing,” says Rosemarie Howe, the interior designer who worked with Ms. Clinton on the project from 2003 to 2006. “We also wanted to open the house and all of its interior rooms to this beautiful back garden.”

“I spend every bit of time that I can [here],” says Ms. Clinton of the lush and landscaped gardens in the backyard. In fact, the family prefers to entertain outside. “We have lots and lots of outdoor events, hundreds and hundreds of people sometimes,” she says. The pool, which had been completely renovated, sees its fair share of activity, too. Ms. Clinton, who is an avid swimmer, uses the pool along with family and friends. She adds, “Even while we’re not there, we have friends with kids who come over and use it.” Behind the pool sits a poolhouse which had been imagined as a guesthouse for Ms. Clinton’s mother, Dorothy Rodham. (She ultimately decided to settle in a bedroom in the main house.) The lantern at its entrance is a design by South Carolina firm The Urban Electric Company.

Working alongside architect Donald Lococo and landscape gardener Lila Fendrick, Howe set out to create what is now the showpiece of the property: a sun-filled conservatory living area that extends off the back of the original footprint. Additional work on the ground floor allowed for a more organic flow and function, and tweaks upstairs yielded larger hangout spaces for the family. “It was kind of this Ozzie and Harriet house and it had never been updated. The bathrooms were sort of '50s,” says Howe. “The kitchen was functional but very outdated, too. The people who had lived there before were very tall, so counters and things were quite high.”

Having also worked on Ms. Clinton’s guesthouse in Chappaqua, New York, and her State Department office, Howe is keenly in tune with the former Secretary of State’s aesthetic. “The Clintons have a lovey connection to their past,” explains Howe, who not only selected the home’s furniture but also worked to place countless mementos and artworks the couple had collected over decades in the spotlight, including a large brushstroke painting by James Nares in the solarium. “But it’s all with a total lack of pretense," she says. "A key part for [Ms. Clinton] is that she wants people to come in the door and not feel intimidated. She wants a comfortable place for everyone to sit.”