The move came after Pär Nuder, a close ally of Göran Persson, was edged out last week when it became clear that Persson’s successor Mona Sahlin no longer valued his services in the post.
Commenting on the vote, Sahlin said that the change felt “secure and correct”.
Östros, who said he was honoured to have received the job, wasted no time in launching an attack on the centre-right government.
“The government has polices that won’t survive rainy days; they are founded on sunny days and a booming economy,” he said.
Östros added that the government’s tinkering with labour market policy would lead to problems if the economy was hit by a downturn.
Pär Nuder embraced Östros and made him a gift of a pair of braces and a belt, accessories once worn by former Social Democratic finance minister Gunnar Sträng.
“He was the natural choice,” said Nuder of his successor.
According to Nuder, he and Östros are practically indistinguishable on matters of economic policy.