His La République en Marche (Republic on the Move or LREM) with its MoDem allies is expected to win most seats.
Traditional parties are urging voters to back Mr Macron's rivals to stop a monopolisation of power.
President Macron formed his party just over a year ago, and half of its candidates have little or no political experience.
They include a retired bullfighter, a Rwandan refugee and a mathematician.
A party needs 289 seats to control the 577-seat National Assembly. LREM is predicted to win more than 400.
What happened in part one?
In the first round Mr Macron's LREM and MoDem won 32.3% of the vote.
The centre-right Republicans had 21.5%, while the far-right National Front (FN) had 13.2%, followed by the far-left La France Insoumise (France Unbowed) on just over 11%.
The Socialists, previously France's ruling party, and their allies won just 9.5%.
However, the turnout was low, despite claims that President Macron had re-energised the voting public.
Analysts said it reflected a sense of resignation among his opponents.
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