Democratic presidential candidate Pete Buttigieg (L) and Senator Bernie Sanders (R) Photograph:( AFP )
Buttigieg edged out Sanders with 26.2 per cent of state-delegate equivalents.
The Iowa Democratic Party declared the final results after a long delay due to technical glitches.
It was a neck-and-neck between Buttigieg and sanders, in the first contest to pick a Democratic nominee to challenge Republican President Donald Trump in the November polls.
Sanders who was among the leading democratic candidates in 2016 finish an at narrow second with 26-point-1 per cent equivalents.
Former US Vice President Joe Biden's disappointing performance was as surprising as the 38-year old Buttigieg's victory.
Biden has been relegated to the 4th place which is 15.9 state delegates equivalents.
In many counties, he has failed to attain the 15 per cent votes needed to be considered a viable candidate.
Biden who served as the Vice President under Obama was once considered the democratic front-runner.
The results of the Iowa caucus are as follows:
Pete Buttigieg: 26.2 per cent
Bernie Sanders: 26.1 per cent
Elizabeth Warren: 18 per cent
Joe Biden: 15.8 per cent
Amy Klobuchar: 12.3 per cent