Alaska Senator Ted Stevens's conviction for corruption should be overturned, officials from the US justice department have requested, BBC reported.
Mistakes made by prosecutors during his trial render the conviction invalid, the officials said.
In October 2008, a jury found Mr Stevens, a Republican, guilty of lying about gifts and free home renovations he received from an oil company.
Mr Stevens went on to lose his Senate re-election battle the following month.
He was the longest-serving senator, having first entered the chamber in 1968.
Prosecutors made a number of errors during the trial, officials said, the chief among which was the failure to make available notes of a crucial interview in which a witness made a statement that contradicted evidence he gave later under oath.
The prosecutors who made the error have been removed from the case and placed under investigation.
A judge will hear the justice department's request on Tuesday, and is expected to grant the motion to overturn Mr Stevens's conviction.
"I always knew that there would be a day when the cloud that surrounded me would be removed," Mr Stevens said in a statement.
"That day has finally come. It is unfortunate that an election was affected by proceedings now recognised as unfair."
The BBC's Jon Donnison in Washington says the high profile case clearly led to Mr Stevens losing his seat and gave the Democrats an important addition to its ranks in the US Senate.
But President Obama's new Attorney General Eric Holder is sending a message that Justice Department prosecutors must operate within the law, our correspondent adds.