The centrist leader had demanded the parliamentary vote in an attempt to end weeks of speculation about the stability of his reshuffled government, which he and President Francois Hollande purged of three rebel leftist ministers last month.
The vote tally showed 269 deputies backed Valls with 244 against. As expected, 32 in his Socialist Party abstained in protest at plans to make 50 billion euros ($65 billion) of public spending cuts in the next three years while easing taxes for business.
Opposition leaders pounced on the fact that the high number of abstentions meant Valls had failed to achieve an absolute majority of 289 votes in the 577-seat assembly, warning that he would struggle to win parliamentary backing for the planned reforms.
"This is more than a warning ... his days are numbered," Christian Jacob, leader of the conservative UMP party in parliament, said directly after the vote.
In a speech designed to placate his Socialist Party while pushing pro-business reforms that have earned comparisons with former British premier Tony Blair, Valls earlier told the assembly his goal was to improve life for all French.
"Reform doesn't mean destroying our social model," Valls said of France's highly protective labour code and a welfare state and health service that are among the most comprehensive and expensive in the world.
"We must adapt and reinvent this model but it's not dead, it's not outdated," he added.
With Hollande's approval rating at just 13 percent due to public dismay about the weak economy and his messy private life, the government is banking on the more popular Valls to carry through the reforms.
Yet a survey by pollster Ipsos in Le Point magazine on Monday showed his popularity was being contaminated by the sense of disarray surrounding Hollande. The premier's rating fell four points to 30 percent and 63 percent of respondents said they had an "unfavourable view" of what he has done so far.

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