Results from the Iowa Republican Party showed on Monday night that Trump had received 51% of the votes in Iowa.
Florida Governor Ron DeSantis trailed in second place with 21% of the vote and former US Ambassador to the United Nations Nikki Haley trailed in third with 19% of the vote.
The Republican caucusing is being held at 1,600 polling stations across Iowa.
Donald Trump said in a speech after winning the Iowa caucus vote that it is time for Americans to come together and "straighten out the world."
"I really think this is the time now for everybody in our country to come together. We want to come together, whether it's Republican or Democrat or Liberal or Conservative, it would be so nice if we could come together and straighten out the world, straighten out the problems and straighten out all of the death and destruction that we're witnessing," Trump said on Monday night.
Trump also congratulated fellow contenders for the Republican nomination - Florida Governor Ron DeSantis, former US Ambassador to the United Nations Nikki Haley and entrepreneur Vivek Ramaswamy for the results they achieved n the vote.
Results from the Iowa Republican Party showed that Trump had received 51% of the votes, DeSantis trailed in second place with 21% of the vote and Haley trailed in third place with 19% of the vote.
Iowa will send 40 delegates to the Republican National Convention, which is scheduled for July 15-18 in Milwaukee, Wisconsin. A total of 2,500 people will vote at the convention. To win the Republican party presidential nomination, a candidate needs the votes of 1,215 delegates.
The final results of the Iowa caucuses are expected later on Monday night.