Donald Trump will sign a package of stiff financial sanctions against Russia which bar him from easing the penalties, the White House has said.
Moscow responded to the news quickly, ordering a cut in the number of US diplomats in Russia and closing the US embassy's recreation retreat.
The US president's willingness to support the measure is a remarkable acknowledgement that he has yet to sell to his party on his hopes for forging a warmer relationship with Moscow.
His vow to extend a hand of co-operation to Russian president Vladimir Putin has been met with resistance as sceptical politicians look to limit the president's leeway to go easy on Moscow over its meddling in the 2016 presidential election.
The Senate passed the sanctions bill 98-2, two days after the House of Representatives pushed the measure through by an overwhelming margin, 419-3. Both were veto-proof numbers.
The White House initially wavered on whether the president would sign the measure into law, but in a statement late on Friday, press secretary Sarah Huckabee Sanders said Mr Trump had "reviewed the final version and, based on its responsiveness to his negotiations, approves the bill and intends to sign it".
Never in doubt was a cornerstone of the legislation that bars Mr Trump from easing or waiving the additional penalties on Russia unless the US Congress agrees.
The provisions were included to assuage concerns that the president's push for better relations with Moscow might lead him to relax the penalties without first securing concessions from the Kremlin.
The legislation is aimed at punishing Moscow for interfering in the 2016 presidential election and for its military aggression in Ukraine and Syria, where the Kremlin has backed President Bashar Assad.
It also imposes financial sanctions against Iran and North Korea.
Before Mr Trump's decision to sign the bill into law, Republican senator John McCain said its passage was long overdue, a jab at Mr Trump and Republican-controlled Congress.
Mr McCain, chairman of the Armed Services Committee, who has called Mr Putin a murderer and a thug, said: "Over the last eight months what price has Russia paid for attacking our elections? Very little."
Russia's Foreign Ministry said it was ordering the US embassy in moscowa to reduce the number of its diplomats by September 1.
Russia will also close down the embassy's recreational retreat on the outskirts of Moscow, as well as warehouse facilities.
Mr Trump had privately expressed frustration over Congress' ability to limit or override the power of the president on national security matters, according to administration officials and advisers.
But faced with heavy cross-party support for the bill in the House and Senate, the president had little choice but to sign the bill into law.
Mr Trump's communications director Anthony Scaramucci suggested on Thursday that the president might veto the bill and "negotiate an even tougher deal against the Russians".
But Republican Bob Corker, chairman of the Senate Foreign Relations Committee, said it would be a serious mistake and if Mr Trump rejected the bill, Congress would overrule him.
Nevertheless, signing a bill that penalises Russia's election interference marks a significant shift for Mr Trump.
He has repeatedly cast doubt on the conclusion of US intelligence agencies that Russia sought to tip the election in his favour and has blasted as a "witch hunt" investigations into the extent of Russian interference and whether the Trump campaign colluded with Moscow.
The 184-page bill seeks to hit Mr Putin and the oligarchs close to him by targeting Russian corruption, human rights abusers, and crucial sectors of the economy, including weapons sales and energy exports.