Michael McFaul said the ban was "because of my close affiliation with [President Barack] Obama".
Mr McFaul said he was preparing to visit Russia "to do [Hillary] Clinton transition work" before Donald Trump won the US election.
Russia's foreign ministry confirmed the ban, Russian news agencies reported.
In a public post on Facebook, Mr McFaul said: "Was told that I am on the Kremlin's sanctions list because of my close affiliation with Obama. I will take that as a compliment! The US sanctioned Russians close to Putin.