While often the subject of the President's ire - he even privately discussed resigning a year ago after reports emerged that he had floated wearing a wire to surveil the president - Rosenstein had nothing but praise for his boss in his letter on Tuesday. His successor, deputy transportation secretary Jeffrey Rosen, has already been nominated by Trump and is awaiting Senate confirmation. The official said they were expecting the letter this week.
But Barr asked Rosenstein to stay on while Robert Mueller's investigation wound up, and Rosenstein obliged. His exit will leave the department without the Justice Department leader most closely aligned with the probe as officials grapple with continued public and congressional scrutiny of the special counsel's findings and the department's handling of the report.
Democrats have directed most of their anger at Barr for how he chose to selectively release certain details of the Mueller report before making it public and for his decision to declare Trump had not obstructed justice.
Integral to the start of the probe, Rosenstein was also present for the very end.
In his letter, Rosenstein thanked President Trump for appointing him to the job and "for the courtesy and humor you often display in our personal conversations".
Practice abandoned after drain cover wrecks Williams vehicle
Race officials made a decision to end the session as track repairs were carried out, the F1 site reported. He was unharmed but the session, just 10 minutes old, was hastily red-flagged.
But he goes on to quote former attorneys general about the importance of the law being non-partisan, and he writes himself, "the Department bears a special responsibility to avoid partisanship". But it's largely an anonymous, behind-the-scenes position.
Mr Rosenstein appointed Robert Mueller in May 2017 following the recusal of then-Attorney General Jeff Sessions and oversaw much of his work.
The White House initially cited the memo as justification for the firing, but Mr Trump has said he was thinking of "this Russian Federation thing" when he fired Mr Comey.
The deputy attorney general came under withering attack from Republicans on Capitol Hill, who accused him of withholding information from Congress and dragging out the investigation.
Rosenstein, 54, who worked at the justice department for almost 30 years, came under an unusually bright spotlight because of his role initiating the special counsel Robert Mueller's investigation into Russian interference in the United States election. "The Department of Justice pursues those goals while operating in accordance with the rule of law". Citing anonymous sources, the paper said Mr Rosenstein had suggested secretly recording the President in order to prove he was dysfunctional and had argued it was permitted in line with the 25th amendment of the constitution.