Fernandez is a lawyer and senator who followed her husband as he rose from an obscure governorship to the presidency, drawing comparisons to Sen. Hillary Rodham Clinton. She will bring a feistier and more glamorous style to the Pink House, Argentina's presidential palace, in which she has already spent the last four years.
But it is unclear how much change she will bring. Analysts say her strong win gives Fernandez an opportunity to right the problems of her husband's administration, including high inflation, an energy crisis and a shrinking budget surplus. Some warned her not to see it as an endorsement of all of Kirchner's policies.
In her victory speech Sunday night, Fernandez, 54, pledged not to let that happen.
"We have won amply," she said. "But this, far from putting us in a position of privilege, puts us instead in a position of greater responsibilities and obligations."
With more than 96 percent of polling places reporting, Fernandez had 45 percent of the vote, compared with 23 percent for former lawmaker Elisa Carrio and 17 percent for former Economy Minister Roberto Lavagna. Eleven others split the rest. Fernandez needed 40 percent and a margin of 10 percentage points over the runner-up to avoid a runoff.
Carrio spokesman Matias Mendez said seven parties had filed a complaint alleging missing or stolen ballots. One representative of the ruling party was arrested on suspicion of trying to vote twice, and a judge extended voting by an hour in the capital because many polling stations opened late.
But no major problems were reported as Argentina's 27.1 million registered voters, in addition to the presidency, filled dozens of House and Senate seats and nine governorships. Vice President Daniel Scioli won the race for governor of Buenos Aires province, the country's second most powerful post.
Kirchner oversaw a dramatic recovery from a crippling 2001 economic crisis, repaying Argentina's entire $9.5 billion debt to the International Monetary Fund, although critics say Argentina would be riper for sustainable development if he had better managed the income from soaring commodity prices.
But while his accomplishments helped Fernandez win the presidency, they won't help her succeed in office.
"Her husband had the advantage of everyone saying, `He got us out of the crisis,"' said Michael Shifter of the Inter-American Dialogue think tank in Washington. "Well, they can't say that about her, because they already got out of the crisis."
Riordan Roett, director of Western Hemisphere studies at Johns Hopkins University, predicted a troubled term because of rising inflation, frozen energy prices and defaulted debt to rich nations.
"This is a dynasty-in-waiting, but it will collapse as they all do if she can't get a team together to differentiate herself from Nestor Kirchner," he said.
Fernandez ran an unorthodox campaign, refusing to debate and spending much of the time abroad in photo-ops with world leaders. Her chic European dresses and designer bags drew comparisons with Evita Peron, another fashion-conscious and politically influential Argentine first lady.
She will be Argentina's second female president; Isabel Peron - who married Juan Peron after Evita's death - was his vice president when he died in 1974, and served for 20 chaotic months before a military coup ousted her.
As for Kirchner, he has said he'll be happy as "first gentleman" after he hands his wife the presidential sash and scepter on Dec. 10. But few expect him to fade too far into the background - and some even suspect the couple is plotting to reverse roles again in 2011.
"That's the million-dollar question: What will Kirchner do after handing over power?" said political scientist Gustavo Martinez Pandiani. "No one believes he's going to be in his pajamas and slippers, waiting for his wife to come home so he can say, `Hi. How was your day?"'