The move, which sent the Russian stock index to an all-time high, has watered down the toughest penalties imposed since Moscow's 2014 annexation of Crimea, following a lobbying campaign in the United States that lasted nearly 10 months.
Sanctions relief for Rusal, the world's second-largest aluminium producer, will remove a source of uncertainty from the market.
Aluminium prices surged last April when the US Treasury imposed the financial restrictions but have fallen back in expectation of the sanctions being lifted.
On Jan. 28, the LME said it had lifted its suspension on storing Rusal-produced metal in LME-approved warehouses with immediate effect.
The No. 2 House Democrat, Steny Hoyer, wrote to Treasury Secretary Steven Mnuchin on Thursday and asked him to wait to lift the sanctions saying Congress still had many questions about the decision.
On December 19, the Treasury Department notified Congress of its intent to lift the sanctions saying the companies were sanctioned due to their ownership and control by oligarch Oleg Deripaska, not for the conduct of the companies themselves, CNN reported. "This represents just one more step in undermining the sanctions law, which President Trump has obstructed at every opportunity, while Russian aggression remains unabated".
Congressional Democrats have tried to block Treasury's action, citing concerns about the Trump administration's motives at a time when Special Counsel Robert Mueller is continuing his investigation of Russian interference in the 2016 presidential election and possible connections to the Trump campaign.
That action, it said, ensured that most directors on the En+ and Rusal boards would be independent, including Americans and Europeans who had no business, professional or family ties to Deripaska or any other person designated for sanctions.
"The companies have also agreed to unprecedented transparency for Treasury into their operations by undertaking extensive, ongoing auditing, certification, and reporting requirements", the department's statement said.
After the Treasury announcement, Rusal said its chairman, Jean-Pierre Thomas, had resigned as part of the deal to lift the US sanctions.
Advocates for keeping the sanctions had argued that Deripaska, an ally of Russian President Vladimir Putin, retained too much control over the companies to lift sanctions imposed in April to punish Russia for actions including its annexation of Ukraine's Crimea, efforts to interfere in US elections and support for Syria's government in its civil war.
EN+ Chairman Lord Barker said on Sunday night that the sanctions removals mark a turning point for the company, calling the moves "a clear victory for muscular corporate governance".
In a separate statement, En+ announced the addition of seven independent directors to its board, as well as a securities swap with Ivan Glasenberg's Glencore.
Trump administration officials, and many Republicans who had supported lifting the sanctions, had said they were anxious about the effect on the global aluminum industry. Rusal, a move that will provide relief to the global aluminum market.
"All sanctions on Deripaska continue in force", the statement added.