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. 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 president 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.
Fourth woman in government
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).
Although the People's Party put up Toni Bortoluzzi to draw attention to the fact they have only one seat in cabinet while being the second largest party in parliament, he was never likely to win.
It is not yet certain which portfolio Micheline Calmy-Rey will take over. The cabinet will allocate ministerial departments on December 11.
Dreifuss has been a member of the government since 1993. She announced her resignation on September 30.
Under the Swiss system, parliament chooses cabinet ministers in a secret ballot, and parliamentarians are free to nominate any candidate they please - irrespective of whether they are on the official ticket.
Cabinet seats are allocated according to a convention dating back to 1959 - commonly known as "the Magic Formula."
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.
The Social Democratic Party has nominated two candidates to contest the vacant cabinet seat.
Cabinet seats are divided among the four main political parties in a power-sharing arrangement known as the Magic Formula.
The outgoing Social Democrat minister, Ruth Dreifuss, should be replaced by a politician from the same party.
The vote is a free one conducted by a secret ballot of all members of parliament.
The new cabinet minister will have to secure at least half the available votes plus one.