The billionaire businessman beat rival Ted Cruz in the latest primary election in Indiana winning 51% of the vote versus Mr Cruz's 36%.
The win forced Ted Cruz - the last remaining rival to Donald Trump - to pull out of the Republican race to be selected to run for the presidency.
While Donald Trump has not yet secured enough delegates to be formally selected as the Republican candidate to battle the Democrats for the White House, his path to securing the necessary amount is now clear because no one else is left to challenge him.
The Indiana victory comes after a string of heavy wins in other primaries across the United States which have surprised some political commentators who gave the entrepreneur little chance of success before the Republican race began.
Mr Trump said after his Indiana victory: "I have met some of the most incredible competitors that I have ever competed against right here on the Republican party.
"We started off with that 17 [competitor] number and just so you understand Ted Cruz - I don't know if he likes me or if he doesn't like me - but he is one hell of a competitor.
"He is a tough, smart guy and he has got an amazing future."
Donald Trump has been criticised in the past for remarks which some have deemed to be insulting to Mexicans, women and disabled people.
He's also been criticised by some for supporting the torture of terror suspects and for wanting to ban Muslims from entering the United States until states can "figure out what the hell is going on" regarding the link between Islam and terrorism.