Ellen Tauscher, a centrist Democrat from California who served in Congress for 13 years before becoming a diplomat in the Obama administration, where she helped negotiate a treaty with Russia that limited missiles and nuclear warheads, died on Monday in Palo Alto, Calif. She was 67.
Her family, in a statement on Facebook, said the cause was pneumonia. The statement also said that Ms. Tauscher had survived esophageal cancer in 2010.
Ms. Tauscher made her mark not only on national politics and diplomacy but also, before that, on Wall Street, where she was an investment banker and bond trader for 14 years, at firms including Bear Stearns and Drexel Burnham Lambert. At 25, she was one of the first women to hold a seat on the New York Stock Exchange, where she served from 1977 to 1979, and the youngest woman ever. She was also an officer on the American Stock Exchange.
She ventured into politics in 1992 as co-chairwoman of the first Senate campaign of her friend Dianne Feinstein, in a special election to fill the seat vacated by Pete Wilson, who had been elected governor. Two years later, she was co-chairwoman of Senator Feinstein’s successful campaign for election to a full term.
Ms. Tauscher was elected to the House of Representatives in 1996 to represent a newly created district in the San Francisco area. In a decidedly conservative district with more registered Republicans than Democrats, she was an underdog against the strongly conservative Republican incumbent, William P. Baker.
Ms. Tauscher campaigned in favor of access to abortion and increased spending on education. At the same time, she pledged to work against wasteful spending. Perhaps most crucial, she was in favor of gun-control legislation, while Mr. Baker had voted to repeal a federal ban on assault weapons.
That vote, The East Bay Times of Walnut Creek, Calif., noted on Tuesday, worked against Mr. Baker when a constituent, whose wife was among eight people killed by a gunman, campaigned on behalf of Ms. Tauscher.
After her victory, Ms. Tauscher said: “My message throughout this campaign was one of moderation and common sense. I want to go back to Washington and stand in the middle — where most Americans stand.”
She won her next two elections by more comfortable margins. Beginning in 2002, after her district had been redrawn by the California Legislature to the benefit of Democrats, she was re-elected easily.
During her first term, she was assigned to the National Security Committee, later renamed the Armed Services Committee. She eventually became chairwoman of the panel’s Strategic Forces Subcommittee. Her interest in nuclear weapons and arms control was attributable in part to the presence in her district of the Lawrence Livermore National Laboratory, a center of nuclear weapons research; the California campus of Sandia National Laboratories; and Travis Air Force Base.
In Congress, she often demonstrated that she was not in lock step with her fellow Democrats. Sometimes she sounded like a Republican, as when she spoke in favor of cutting taxes, especially the estate tax and the so-called marriage penalty, which can occur when two people with equal or similar incomes marry, causing them to pay more in taxes than if they had remained single.
But she opposed the $1.6 trillion tax cut that President George W. Bush proposed, which Congress approved, in 2001.
When Representative Nancy Pelosi of California ran for Democratic minority whip in 2001, Ms. Tauscher backed her more moderate rival, Representative Steny H. Hoyer of Maryland.
In 2003, she voted to support the war against Iraq, though she became skeptical after several postwar visits to the country convinced her that efforts to build a new country after the overthrow of Saddam Hussein were not going well.
Ms. Tauscher resigned her House seat on June 26, 2009, when she was confirmed by the Senate as under secretary of state for arms control and international security, a post to which she was appointed by Secretary of State Hillary Clinton.
Ms. Tauscher played a key role in achieving the New Strategic Arms Reduction Treaty of 2010, which placed limits on bombers, launchers and submarines as well as nuclear warheads. The treaty, which expires in 2021, sent American and Russian nuclear arsenals to their lowest levels in nearly 60 years.
She served as under secretary until 2012.
“She made America and the world safer through her work on arms control at the State Department,” Ms. Clinton said in a statement after Ms. Tauscher died.
Ellen O’Kane was born in Newark on Nov. 15, 1951, the oldest of four children of a grocer and his wife, a secretary, and grew up in Harrison, N.J. She received a bachelor’s degree in early childhood education from Seton Hall University in 1974.
After she prospered on Wall Street, she created the Tauscher Foundation, which donated $200,000 to elementary schools in California and Texas to buy computer equipment for students, according to her House of Representatives biography. She also founded a service to screen prospective child-care providers.
Survivors include a daughter, Katherine, from her marriage to William Tauscher, which ended in divorce, as did a second marriage, to James Cieslak. Complete information on survivors was not available.
Asked in 2013 if she was comfortable with a Democratic Party whose philosophy was to the left of hers and becoming more so, Ms. Tauscher said: “I don’t want to move my left to the center. I want my left to stay where they are. But I want them to know that we need a center.”