PARIS — Freshly elected to the French presidency, Emmanuel Macron now faces an equally difficult Act II: securing the parliamentary majority he needs to make good on his campaign promises to lift France out of economic gloom.

With legislative elections just five weeks away, the start-up political movement the 39-year-old former investment banker launched one year ago on his meteoric ride to become France’s youngest president lost no time Monday in girding for the crucial mid-June election battle.

Without a working majority, Macron could quickly become a lame-duck president, unable to push through labor reforms and other measures he promised to the broadly disgruntled electorate — shown by a record result for his defeated far-right opponent, Marine Le Pen, and a record number of blank and spoiled ballots in Sunday’s runoff vote.