Anatoly Antonov had been recalled to Moscow for consultations in March after Joe Biden labelled Vladimir Putin as "a killer" in an explosive interview.
Russia's envoy to the United States flew to Washington on Sunday after presidents Joe Bien and Vladimir Putin agreed to return previously expelled ambassadors to their posts at a summit in Geneva this week.
Anatoly Antonov had been recalled to Moscow for consultations in March amid tensions between Russia and the US.
The diplomat's flight took off at 09:20 local time (06:20 GMT) from Moscow's Sheremetyevo airport to New York before connecting to Washington, Russian news agencies reported.
"Given the results of the meeting between the two presidents, I am counting on constructive work with my American colleagues to build relations on an equal and pragmatic footing," Antonov told Ria Novosti news agency.
US Ambassador in Moscow John Sullivan, who left Moscow in April, also announced he would be back in the Russian capital "soon."
"After an important summit, I look forward to returning to Moscow soon," he said, according to the spokesman of the US embassy in Russia.
He cited "strategic stability, human rights, a stable and predictable relationship with Russia" as his axes of work.
Diplomatic relations between Moscow and Washington deteriorated rapidly after Biden took office in January. The American President accused Russia of serial cyberattacks and electoral interference in the US.
In March, Russia recalled Antonov after Biden labelled Putin as a "killer" in an explosive interview.
Sullivan announced a month later that he would return to Washington for consultations.
Tensions appeared to ease as Biden met his Russian counterpart in Geneva on Wednesday. Biden said the tone was "good" and "positive", while Putin called the encounter "constructive".
Besides their agreement to return their chief diplomats to Moscow and Washington, the two leaders decided working on a plan to solidify their countries’ last remaining treaty limiting nuclear weapons.
But the summit also highlighted deep differences on human rights, cyberattacks, election interference and more.