John Benjamin O’Sullivan of Washington, D.C., and West Tisbury, died suddenly on April 23 at the age of 66. Born in Los Angeles, where his mother was living while his father was serving at the front in World War II, John spent his earliest years on the beach at Malibu and grew into an expert body surfer at Windy Gates on the Vineyard.

He lived in Washington until he was seven, when his family moved to Mamaroneck, N.Y. John’s wit was apparent from the time he could talk. Answering his parent’s phone, John was overheard informing the caller with irritation: “I am only four, you fool.” He was a talented musician, serving as church soloist, playing the trumpet and cornet and winning a local French horn competition.

John graduated from Riverdale Country School, where he began fencing. His weapon was the saber. He received a bachelor of arts degree from the Woodrow Wilson School of Public and International affairs at Princeton University, the alma mater of his father and grandfather, and subsequently both daughters. He was captain of the fencing team at Princeton. The team won the NCAA championship. And like his father, he graduated from New York University Law School.

He worked on the presidential campaigns of Eugene McCarthy and George McGovern and was a principal organizer of the Viet Nam moratorium. With his colleagues from those campaigns, John held two retreats at the O’Sullivan family home in West Tisbury to plan the political future of the country. Participants included Taylor Branch, John Shattuck, David Hawk, Rick Stearns, Tony Podesta and Bill Clinton.

After law school, John served as executive director of Grassroots Action in New York, a consumer advocacy organization, and worked for the law firm of Surrey Karasik and Morse, where he represented a sweat equity building in lower Manhattan in a groundbreaking case that enabled the tenants to sell electricity generated by a rooftop windmill to Consolidated Edison. He was appointed chief advisory counsel to the Federal Energy Regulatory Commission under the Carter Administration. He was the “principal architect of the rules implementing the PURPA [Federal Public Utilities Regulatory Policy Act of 1978] program,” according to the International Financial Law Review. This legislation opened the way for alternative energy companies and required public utilities to buy their electricity.

From 1981 to 2009, he was senior counsel at the Chadbourne Parke law firm in Washington. According to a former colleague and mentee who spoke at John’s memorial in Washington on May 7, John helped “turn on the lights” in Uganda, Tegucigalpa, Pakistan, rural Mexico and many other countries by developing financing and delivery systems for states without the resources to provide electricity consistently to their citizens. He was frequently cited as a leading lawyer in the U.S., and was called a super lawyer and global leading lawyer for his expertise in energy regulation.

He married Susan Williams, a China scholar, in 1973. Their first daughter, Sarah, was born shortly after their arrival in Washington; Katharine came five years later. John took great pride in Susan’s accomplishments, dignity and beauty and delighted in his daughters and Sarah’s husband, Jason McCullough — and recently in his dog Maggie, the most intelligent and humorous dog who ever lived. John said Maggie was, like all his girls, beautiful and athletic. Unlike them, however, Maggie is not fluent in Chinese.

John’s father, Ben, was an international tax and literary estate lawyer whose clients included Aristotle Onassis, Hannah Arendt and Mary McCarthy. His mother published her first novel at 19; she is currently working on a novel about her childhood in Hollywood. Her brother and John’s uncle, Budd Schulberg, won an Oscar for On the Waterfront. John’s younger sister, Dr. Chris O’Sullivan, is a criminology researcher in New York city. Susan is a senior advisor in the Bureau of Human Rights, Democracy and Labor at the State Department; Kate is the assistant to the chief operating officer at Bridgewater Associates, an investment firm in Westport, Conn.; and Sarah and Jason McCullough are associates at O’Melveny & Myers and Davis Polk, respectively.

John began spending at least part of every summer on the Vineyard in 1949. His parents rented various houses in Chilmark and Menemsha until 1968, when they bought the Spaulding Camp on the Tisbury Great Pond. During the family’s Vineyard summers, John taught tennis at what was then known as Tommy Sherman’s court at the bottom of Flanders Lane, worked at Humphreys, yielding a cache of doughnut holes and tales of doughnut disasters, and sailed with his friend Michael Kortchmar. When John’s daughters came along, he loved to take them to the fair, by boat to the cut, to grill hot dogs at the beach and bluefish at home, and always to regale his friends with stories and tease them with jokes. He was wildly enthusiastic about if exhausted by Sarah’s wedding on Martha’s Vineyard two years ago, and pleased that Sarah and Jason recently bought a house near his and Susan’s home in Washington. Even before Sarah and Kate were grown, John debated various plans to expand the guest house to allow him to spend time on the Vineyard with his children and future grandchildren.

On John’s last day, he took on a new client, fielded calls from headhunters and continued his work leading legal opposition to the D.C. zoning board’s approval to a large development project in his Cleveland Park neighborhood. Susan tried to wake him the next morning to take Maggie to meet her best dog friend at the park. His friends and neighbors were stunned that someone so full of life and anticipation of the future had slipped away. His doctor determined the cause was a heart attack.

He was interred at the West Tisbury cemetery on Thursday, April 29, near his father. The graveside service was attended by John’s family and close friends, including West Tisbury neighbors Arnold Fischer and Eleanor and Sarah Neubert, Phyllis Segal of Chilmark, and cousin Benn Schulberg, whose mother’s family, the Langmans, are longtime summer residents of Menemsha. At the memorial service in Washington, John’s life was celebrated with classical instrumental music, jazz and folk music, and a cappella singing by Yale Law School professor Drew Days and president of Central European University John Shattuck; with descriptions of his important legal and political work, and with tales of his stories, jokes and bonhomie. A line repeated by his friends was that words John never spoke were, “Stop me if you’ve heard this one before.” John had no plans to stop. Susan, Sarah and Kate are devastated. “He was the center of our lives,” and they were the center of his.