He also announced on Friday that he would order about 1,500 additional troops to the Middle East to increase protection of those American forces already there.
The new deployment is less than what hardliners in the White House were said to have wanted, and below what commanders in the region were considering, the New York Times reported.
The deal would "deter Iranian aggression and build partner self-defence capacity" of US allies, Secretary of State Mike Pompeo said in a statement.
"These sales will support our allies, enhance Middle East stability and help these nations to deter and defend themselves from the Islamic Republic of Iran," he added, referring to heightened tensions with Tehran.
Pompeo's notification to lawmakers about the move effectively give the Trump administration a green light to conclude the sale and transfer of bombs, missile systems, semi-automatic rifles, drones and repair and maintenance services to aid the Saudi air fleet, and precision-guided munitions that lawmakers fear Saudi Arabia may use against civil in Yemen's civil war.
Some Democrats accused Trump of bypassing Congress because the sale of weapons would have been strongly opposed on Capitol Hill.
The move quickly garnered opposition. Democratic Senator Robert Menendez, who sits on the Foreign Relations Committee, accused Trump of "granting favours to authoritarian countries".
"(He) has failed once again to prioritize our long term national security interests or stand up for human rights," Menendez said in a statement.
Foreign Relations Committee Chairman James E. Risch said he was "reviewing and analyzing the legal justification for this action and the associated implications".
Traditionally, the administration must notify Congress when it contemplates a new arms sale, giving lawmakers the opportunity to review deals and block those they find objectionable.
In each of his letters notifying lawmakers of the decision, Pompeo stated that he had "determined that an emergency exists which requires the proposed sale in the national security interest of the US and thus, waives the congressional review requirements" - without noting the nature of the emergency or offering details about it.
In his letters, he added that the government had "taken into account political, military, economic, human rights, and arms control considerations".
Lawmakers have frequently questioned the Trump administration's approach to national security policy and its track record on human rights.
In particular, Trump and Congress have been at odds over the President's unapologetic embrace of Saudi leaders, despite US intelligence showing that the Saudi Crown Prince was behind the October 2018 killing of kingdom's journalist Jamal Khashoggi.
Iran reacted angrily to the US move, with Foreign Minister Mohammad Javad Zarif calling it "extremely dangerous" for international peace.
( With inputs from IANS )