The vote brings to an end a bitter wrangle between President Sheikh Sharif Ahmed and Somalia's second most powerful politician, Parliament speaker Sharif Hassan Sheikh Aden.
Somali legislators approved the appointment of Prime Minister Mohamed Abdullahi Mohamed on Sunday, voting overwhelmingly for the president's nominee.
The presidency said in a statement that 297 of the 392 members of Parliament present voted with a show of hands in favour of Mohamed, a US-educated former diplomat from the Somali diaspora.
"We will move with full speed to do the people's business. I will very soon form an effective and dedicated cabinet that will put the Somali people first," Mohamed said.
Somalia has been mired in violence and awash with weapons since the overthrow of a dictator in 1991 and the weak Western-backed government controls only parts of the capital.
Western security agencies warn that the lawless nation is a fertile breeding ground for Islamist militants, while the chaos on land has allowed piracy to flourish off its shores.
The vote brings to an end a bitter wrangle between President Sheikh Sharif Ahmed and Somalia's second most powerful politician, Parliament speaker Sharif Hassan Sheikh Aden.
While the dispute was over whether the vote should be a secret ballot or a show of hands as desired by the president, analyst said the rift was really a powerplay between the two men and the blocs they represent.
Analysts say Aden has indirect support from neighbouring Ethiopia while Ahmed has the backing of religious groups within Somalia and the two are battling for influence within cabinet.
Ahmed chose Mohamed to be his new prime minister after his predecessor quit in September, paying the price for failing to rein in a three-year Islamist insurgency.
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