The two countries agreed to split the two-year term on the council yesterday after five rounds of voting earlier this week ended with a tie.
Under the deal, Italy will take up the seat on January 1 and then make way for the Netherlands to take over in 2018.
The arrangement is rare but not unprecedented at the United Nations.
The last split term was in 1964-65 between what was then Czechoslovakia and Malaysia.
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During elections on Tuesday, Kazkahstan was elected to the council for the first time along with Bolivia, Ethiopia and Sweden.
The newly-elected countries will take their place alongside the five permanent council members -- Britain, China, France, Russia and the United States.
The other five non-permanent members are: Egypt, Japan, Senegal, Ukraine and Uruguay.