Scott's endorsement is a blow to fellow South Carolinian, Nikki Haley.
South Carolina Sen. Tim Scott delivered a blow to Nikki Haley ahead of the New Hampshire primary, appearing on stage with former President Donald Trump and endorsing him at his rally in Concord.
"IS THIS TRUMP COUNTRY?" Scott said to the crowd, hyping them up.
Scott touted Trump's immigration, social security and his war against crimes before he declared his endorsement.
"That's why I came to the very warm state of New Hampshire to endorse the next president of the United States, Donald Trump," Scott said.
"We need a president who will unite our country," Scott said. "We need Donald Trump."
Trump thanked Scott, praising him as a "very good man," and a "very respected man" - at the same time disparaged other Republicans for "wasting hundreds of millions of dollars" attacking him. He especially zeroed in on Haley, accusing her of engaging in an "unholy alliance" with "RINOs" and "never-Trumpers."
The endorsement comes just a few days before the New Hampshire primary, set for Jan. 23.
Throughout his campaign, Scott was plagued by rumors that he was vying to be Trump's vice president. Many voters told ABC News that they saw Scott more as a No. 2. Scott slammed the rumors, saying he did not run for president to be in second place.
Scott, who has pledged not to run for reelection in the Senate, told CNBC's "Squawk Box" in December that his endorsement "certainly won't happen this year, if I do it at all." A source confirmed to ABC News that he arrived at this decision only recently.
Haley, who served as South Carolina governor from 2011 to 2017, appointed Scott to the Senate in 2012.
Haley finished in a close second to DeSantis in the Iowa caucuses -- both of whom lost to Donald Trump. She's trailing the former president in New Hampshire polls, according to 538's most recent polling averages. A primary win could be used as a way to build momentum for her campaign as Haley heads into her home state of South Carolina, where she is still polling far behind Trump.
In a statement, Haley drew on Trump's own words to criticize Scott's endorsement.
"Interesting that Trump's lining up with all the Washington insiders when he claimed he wanted to drain the swamp," Haley said in the statement. "But the fellas are gonna do what the fellas are gonna do."
ABC News' Nicholas Kerr contributed to this report.