Alaska Senator Ted Stevens's conviction for corruption should be overturned, officials from the US justice department have requested.
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 Republican senator, having first entered the chamber in 1968.
'Cloud removed'
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.
"it takes two sides to end a war but only one to start one. And those who do not have swords may still die upon them." Tolken
Insofar as the legal system of the US is built, the prosecution out and out cheated. Stevens is as dirty as, well, an Alaskan politician, but I believe it's more important to uphold standards of the justice system.
Now, if only they'd reform the system so this wasn't a get away-free card..
Half-Damned, All Hero.
Tev: You're happy. You're Plotting. You're Evil.
Me: Evil is so inappropriate. I'm ruthless.
Tev: You're turning me on.
It may be a bit of a stretch but given what they were capable of, I wouldn't be surprised if the Bush Justice Department took a dive on purpose.
Either that, or they really were just that incompetent.
Sadly, if we want the federal government to actually follow its own prosecution rules, this one probably has to be tossed.
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