Mitt Romney won the Texas Republican primary on May 29, earning enough delegates to clinch his party's presidential nomination.
In a statement, Romney said: "I am honored that Americans across the country have given their support to my candidacy and I am humbled to have won enough delegates to become the Republican Party's 2012 presidential nominee."
Media reports said the former Massachusetts governor won more than 70 percent of the primary vote, capturing enough of Texas's 155 delegates to meet the benchmark of 1,144 delegates needed for the nomination.
The U.S. congressman from Texas Ron Paul reportedly won 10 percent in his home state, Catholic conservative Rick Santorum 7 percent, and Newt Gingrich, a former speaker of the House of Representatives, 5 percent.
Romney, who came up short in the Republican presidential race four years ago, has been the presumptive nominee for several weeks as the other Republican contenders have mostly dropped out of the primary race.
The delegates are set to formally nominate Romney in August, when the party holds its national convention in Tampa, Florida.
He will challenge Barack Obama for the White House in November elections.
Romney now faces a lengthy to-do list to gird for his duel with Obama, from picking a vice presidential running mate to bolstering his case that the current president has been ineffective in handling the sluggish U.S. economy.
His nomination milestone was clouded by a rehashed controversy over claims by real estate tycoon Donald Trump questioning President Obama's birthplace.
At polls closed, Romney was attending a fundraiser in Las Vegas with Trump, who earlier said there were still lingering doubts about whether Obama was really a natural born U.S. citizen.
Obama's deputy campaign manager, Stephanie Cutter, slammed Romney for lacking "moral leadership" over his appearance with Trump.
Based on reporting by AP, AFP, and Reuters