Micheline Calmy-Rey has become the fourth woman in Swiss history to have a seat in the cabinet.
In the fifth round of voting Calmy-Rey received 131 votes, easily exceeding the overall majority of 100, and clearly defeating the other official candidate for the Social Democrats, Ruth Lüthi, who got 68 votes.
Calmy-Rey's victory was inevitable once the candidate from the Swiss People's Party, Toni Bortoluzzi, dropped out of the running. Most People's Party members of parliament then returned blank votes rather than support a Social Democrat for government.
Accepting her victory, Calmy-Rey said she would use all her strength to serve her country. The Geneva politician succeeds the interior minister Ruth Dreifuss.
In a farewell address before voting began, Dreifuss said Switzerland had the means to tackle poverty. She said she supported an open and competitive market, but not at the expense of human values.
The speaker of the parliament, Yves Christen, paid tribute to Dreifuss as a tireless campaigner for an open and tolerant Switzerland. Members of parliament honoured her with a standing ovation.
Magic formula remains intact
It was a foregone conclusion that the successor to Dreifuss would be a woman - only the fourth in Swiss history to become a cabinet minister after Elizabeth Kopp (1984-1988), Ruth Dreifuss (1993-2002) and Ruth Metzler (since 1999).
The People's Party put up Toni Bortoluzzi to draw attention to the fact they have only one seat in cabinet despite having more members of parliament than the Christian Democrats, who have two government posts.
But Bortoluzzi was never likely to win, because the other major Swiss parties remain committed to Switzerland's "magic formula" system, under which cabinet seats are allocated according to a convention dating back to 1959.
It ensures that there is a representative balance in government among the four main parties with the Social Democrats, the Christian Democrats and the Radicals each taking two posts and the rightwing Swiss People's Party, one.
It is not yet certain which portfolio Micheline Calmy-Rey will take over. The cabinet will allocate ministerial departments on December 11.
Dreifuss served in the Swiss cabinet for over nine years, joining the government in the spring of 1993. She announced her resignation on September 30.
Calmy-Rey clinched the race in the fifth round.
She saw off a challenge from fellow Social Democrat, Ruth Lüthi.
It is not yet clear which portfolio she will have.
She is currently president of the Geneva government.