This is the first veto of Mr Trump's presidency. Several prominent Senate Republicans stood with the Democrats against the president's emergency declaration, including Marco Rubio (R-FL), Mike Lee (R-UT), Mitt Romney (R-UT), Lisa Murkowski (R-AK), Susan Collins (R-ME), and Rand Paul (R-KY).
The statement continued: "The problem with this is that after a revolutionary war against a king, our nation's founders gave to Congress the power to approve all spending so that the president would not have too much power. Yesterday, Congress passed a unsafe resolution that if signed into law would put countless Americans in danger, very grave danger", he said, sitting behind his desk in the Oval Office.
"Congress has the freedom to pass this resolution and I have the duty to veto it", he said, calling it a "Democrat-sponsored resolution".
The renegade conservatives had condemned the emergency declaration for setting up a unsafe precedent for a president while emphasising that they still agreed with Mr Trump's tough border security policies.
U.S. Attorney General William Barr said the president's emergency declaration was legal. The veto will likely put the matter to rest as neither chamber of Congress appears to have the necessary two-thirds majority to overturn Trump's veto.
He said the vote against the president was also a vote "against the America people and their safety and security".
Friday's veto ceremony fulfills Trump's pledged to thwart any effort by the Senate to block his emergency proclamation.
Trump was flanked by border officials and people whose family members were killed by someone who was in the United States illegally. The president has been strong on that.
Republicans who voted against the resolution want money to be there to secure the border, but wanted that to happen through the appropriations process, not through an executive order, said Barrasso, adding that he would have also preferred to do it that way. "Watch, when you get back to your State, they will LOVE you more than ever before!" he said.
The wall was a signature campaign issue for Trump, but he was never able to deliver on his promise to make Mexico pay for it, and the issue languished during his first two years in office. He initially insisted that Mexico would pay for the wall but it has declined to do so.