Authorities spread the election at the weekend in a bid to boost turnout among the 111 million eligible voters and even allowed electronic balloting.
Polls opened on Friday and will close on Sunday.
The Kremlin wants the parliamentary election - the first since the start of the full-scale invasion of Ukraine in 2022 - to underline public support for the war and give a veneer of legitimacy to its action.
It has sought to avoid any political risks by stamping out even the slightest sign of dissent.
"Your choice and resolve will once again demonstrate that millions of people stand behind our fighters, that we are a united people, bound by shared values, historical memory, and love for the Motherland," President Vladimir Putin told the nation before the vote.
The main Kremlin party, United Russia, is all but assured to retain its overwhelming control of the lower house, the State Duma.
Several smaller parties of the "systemic opposition" that vote in sync with the government on all key issues also are expected to retain their presence.
Voters cast two separate ballots, filling half of the Duma's 450 seats by selecting political parties listed on the ballot.
The rest are contested in single-seat constituencies, with voters choosing individual candidates.
The liberal Yabloko party, the only registered political entity that dared to criticise the war, was removed from the ballot in August by Russia's Supreme Court, and only has a few dozen candidates in the single-constituency races.
Additionally, some anti-war politicians have been imprisoned or forced to flee abroad ahead of the campaign.
The election follows a summer of Ukraine's long-range drone strikes on oil refineries that triggered a widespread fuel crisis.
Warehouses belonging to online retailers Wildberries and Ozon also were attacked.
The damage has exacerbated problems for the Russian economy and brought the war home for millions.
For the first time, the parliamentary election includes residents of four Ukrainian regions that Moscow illegally annexed after the war began.
Voting also is taking place in Crimea, the Black Sea peninsula that was illegally annexed by Russia in 2014.
Authorities in Kyiv denounced the voting in the Russian-held areas as illegal and urged foreign governments and international organisations not to recognise the election, warning Ukrainians that taking part in organising the balloting could carry criminal liability.
