Senators unanimously approved the continuation of special powers in Adamawa, Borno and Yobe states in a vote, following a similar backing from the lower chamber House of Representatives last week.
President Goodluck Jonathan requested the extension after calling the continued violence in the three states "daunting" and expressing concern about mounting civilian casualties.
The government first imposed a state of emergency in the three states on May 14 last year in an attempt to crush Boko Haram militants who had been waging an increasingly violent insurgency in the region since 2009.
But despite apparent initial gains in pushing the militants out of urban centres, the attacks continued, increasing in frequency and intensity to the extent that Jonathan requested a further six-month extension in November last year.
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His renewed request came as no surprise, with Boko Haram thought responsible for killing more than 2,000 people, most of them civilians, this year alone.
In approving the request, the senators said they "welcome and endorse the support of the international community" in the operation to rescue more than 200 schoolgirls abducted by Boko Haram from the Borno town of Chibok on April 14.
Nigeria's government and military have come under fire for their tactics in trying to defeat the militants, in particular by using conventional means against an enemy fighting a guerrilla war among the population.
The lawmakers called for "a full military operation to be undertaken on a sustained basis to route the insurgents".
But they also said that non-military means should be considered to address the causes of radicalisation in the impoverished Muslim-majority north, which has been seen as a key factor in recruiting disaffected young men to Boko Haram's cause.