There were 197 abstentions.
The vote in the 500-seat lower chamber of Parliament came a month after her Pheu Thai party won a convincing majority in the July 3 election. It formed a six-party coalition controlling 300 seats in the 500-seat House.
House Speaker Somsak Kiatsuranond earlier said before the House that he would seek royal
endorsement for the newly-elected prime minister once the voting is completed.
Upon receiving His Majesty King Bhumibol Adulyadej's royal endorsement, Ms Yingluck will officially assume the country's top job and authorised to present a cabinet line-up for royal approval.
With an overwhelming mandate from voters, the 44-year-old businesswoman-turned-prime minister will face an uphill task to steer the country out of years of deep-rooted divide and revitalise the country's economy amid fears that the U.S. economy is sliding back toward recession and Europe's debt woes are worsening.
She earlier pledged to restore national reconciliation and unity.
Some Red Shirt supporters who remain loyal to deposed prime minister Thaksin gathered outside the parliament building to show their support for Ms Yingluck.
Mr Thaksin, deposed in a 2006 coup, is barred from politics and lives in exile in Dubai to avoid having to serve a two-year prison term after being found guilty for violating Thailand's conflict of interest law, a conviction that he says is politically motivated.