The nationwide election follows a tumultuous few years that have seen the country seize the Crimea peninsula from Ukraine, plunge into its worst standoff with the West since the Cold War and start a military operation in Syria.
But the Kremlin exerts near-total control and, after a campaign dubbed the most boring in recent memory, a trouble-free victory for ruling United Russia would help smooth the way for Putin to claim a fourth term as president in 2018.
Looming large is the spectre of mass protests over vote rigging that followed the last legislative polls five years ago and grew into the biggest challenge to Putin since he took charge in 2000.
This time round the authorities have made a show of cleaning up the vote by replacing the former scandal-tainted election chief and allowing more genuine opposition candidates to take part.
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But critics insist the Kremlin's media dominance means the vote can never be fair and -- with the 450-member State Duma viewed as a rubber-stamp body that slavishly toes the Kremlin's line -- apathy is widespread.
"But this is my country and I have to express my opinion."
Officials said that by 1500 Moscow time the nationwide turnout stood at almost 33 per cent.
Despite the authorities pledging to crack down on vote-rigging, observers and opposition candidates from around the country posted claims of possible violations including "cruise-voting" -- where people are bussed to vote at multiple polling stations -- and ballot stuffing.
Electoral commission head Ella Pamfilova dismissed claims of widespread fraud but said authorities were probing allegations in the Siberian Altai region and threatened to annul the vote there.
While United Russia had slipped in the polls ahead of the vote it still looks set to scoop the largest chunk of the vote ahead of other parties loyal to the authorities like the Communists and ultra-nationalist Liberal Democratic Party.