The 47-43 vote clears the way for Waltz to attend the UN General Assembly in New York next week, where US President Donald Trump is scheduled to address the annual gathering on Tuesday, Xinhua reported.
During his Senate confirmation hearing earlier this summer, Waltz stressed the need for reform at the UN, including a review of US funding and measures to root out anti-Semitism in the institution, according to an NBC News report.
Waltz had served as Trump's national security adviser since January but stepped down after mistakenly adding a journalist to a private Signal chat with senior national security officials discussing an upcoming strike in Yemen in March.
On March 27, Trump withdrew his nomination of Republican Elise Stefanik to be the US ambassador to the United Nations. Waltz was then nominated by Trump for the post in May.
Former US Ambassador to the United Nations Linda Thomas-Greenfield left her office on Jan. 20 when Trump took office as US president.