The upper house voted 53 to 16 to lock in the spending ceiling.
Center-right President Michel Temer says tough measures are needed to get Brazil's finances back under control, but his austerity policies have prompted violent protests and were criticized last week by a UN expert as "a historic mistake."
Police were out in force in the capital Brasilia to protect government buildings from demonstrators during the upper house vote. An expected protest had not materialized before the Senate rapidly wrapped up its debate.
However, Temer is rapidly losing political clout as he and many of his senior allies fight to survive a slew of corruption allegations.
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Brazilians battered by nearly 12 per cent unemployment and stubbornly high inflation are increasingly angry over the scandals and hostile to the austerity measures.
A poll published today showed that 60 per cent of Brazilians oppose the spending ceiling. Only 24 per cent are in favour, the Datafolha poll published in Folha newspaper said.
Early today, police in the capital restricted access to the area around Congress and said they had confiscated supplies of masks that protesters were planning to wear in case of tear gas.
There have also been violent clashes recently in Rio de Janeiro where less than four months after hosting the Olympic Games, the nearly bankrupt state government is pushing through its own spending cuts and tax hikes.
Businesses in the neighborhood of the local legislature have boarded up their windows in anticipation of more trouble this week.
But as the Senate began debating he defended his far-reaching austerity proposals, saying they were needed to change Brazil for the long term.