In his remarks, the president said there is a lot to be unhappy about and vowed to "never sign another bill like this again" but said he did so as a matter of national security. He called it a “ridiculous situation."
Trump was flanked by Vice President Mike Pence, Defense Secretary Jim Mattis, and Commerce Secretary Wilbur Ross.
Even as he vented distaste for parts of the 2200-page bill that run counter to his agenda, the president repeated previous talking points about reversing deep cuts to military spending and giving a pay increase to troops.
"My highest duty is to keep Americans safe," he said.
As for the border wall, he says the administration will be "getting to work on Monday" with repairing and bolstering border wall. "We have $1.6 billion for the wall starting immediately. It's short-term funding but it's immediately."
Republican leaders spent the past 24 hours selling the bill as a win on border security, despite the fact that it fails to give the president much funding for the wall he promised.
The president tweeted earlier Friday morning that he had been considering a veto.
Shortly after the president fired off his surprise tweet, House Speaker Paul Ryan spoke with Trump around 9:30 a.m. and encouraged him to sign the omnibus, a source familiar with the call told ABC News. The source said they discussed the "wins" in the omnibus, "especially for the military."
Democrats blasted the president for what they see as his hypocrisy on a solution for the fate of some 700,000 Deferred Action for Childhood Arrivals program recipients – young undocumented immigrants brought to the U.S. as children.
“Mr. President, you terminated protections for DACA recipients, you cynically held them hostage for your costly boondoggle of a wall, and you have undercut every bipartisan attempt to fix the mess you created,” Sen. Patrick Leahy, vice chair of the Senate Appropriations Committee, said. “You can fix this. Or at the very least, don’t unilaterally make things worse, yet again.”
ABC News' John Parkinson contributed to this report.