Barr is a renown Republican lawyer who previously served as attorney general from 1991 to 1993. He would replace acting Attorney General Matthew Whitaker, who was tapped to replace former attorney general Jeff Sessions ousted by President Donald Trump in November.
William Barr was approved by the US Senate as the new Attorney General on Thursday.
Now the newly-appointed Attorney General will have to name his deputy and also address the investigation being conducted by Special Counsel Robert Mueller, which he had previously criticised. According to a 19-page legal memo written by Barr earlier, he considered the probe to be "fatally flawed".
In the meantime, media reports suggested that after two years of investigation into Russia’s alleged meddling during the 2016 election, Mueller had no evidence of Trump having colluded with Moscow.
Russia has repeatedly denied interfering in the US election, saying the allegations were made up to excuse the defeat of Trump's campaign opponent as well as deflect public attention from actual instances of electoral fraud and corruption.