Susan Mary Alsop in the 1970s. (Ken Feil/The Washington Post)

At the center of this universe was Susan Mary Alsop, wife of the enormously influential columnist Joe Alsop. She was intellectual, cultured, witty, discreet and observant — but might have faded in history if not for her propensity for writing long, chatty letters.

It was Susan Mary’s correspondence that inspired French author Caroline de Margerie to pen “American Lady,” a new biography of the American socialite. “She was a woman who knew she wanted an interesting life — and set about it,” she told us. “She lived the life but also reported on it.”

A descendant of founding father John Jay, and daughter of a diplomat, Alsop was thrilled by international politics and hobnobbed with many of the 20th century’s biggest names. After a marriage, at 21, to another diplomat, she embarked on stylish life in post-war Paris — and affairs with two British ambassadors — before coming to Washington in 1961 after her husband’s death.

Joseph Alsop (Harry Naltchayan/The Washington Post)

Huh. Why’d she marry him? Even her closest friends still puzzle over it. De Margerie’s theory: He was an old pal and a kind stepfather, and “she liked the life that Joe offered her. . . She became, through Joe, one of the leading ladies of Camelot.”

It was a different era, after all. Today, de Margerie argues, Susan Mary would have made it as a Beltway player in her own right. “I think she would have chosen a career in journalism covering international affairs, or diplomacy.”

The Alsop union worked beautifully for a few years, as they hosted leaders from every side at their home. “That was her purpose: making the political elite understand each other,” said de Margerie. But after Kennedy was killed, the columnist went hawkish on the Vietnam War, damaging his reputation and marriage. They divorced in 1973.

Susan Mary finally made her mark as a writer when she published her letters, and later, three history books. In 1988, she was cited as one of the fifteen most socially prominent people in America. When she died in 2004, she was still one of Washington’s premier hostesses.

She was like a character in a Henry James story, said de Margerie, but with a happier ending: “Susan Mary could have well stepped out of his novels — but she didn’t allow herself to be victimized by society.”

Related: Alsop’s sister-in-law, fellow society doyenne Patricia Alsop, died last week at 86 (obituary), 11/10/12

‘The Columnist’ provides insightful look at D.C. journalist Joseph Alsop (theater review), 4/27/12

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