The judge, however, deferred sentencing until December.
While police say Fossella's BAC was 0 .17, defense attorney Jerry Phillips challenged the accuracy of the Intoxilyzer 5000 machine that was used to measure Fossella's blood alcohol content.
The judge will decide at a Dec. 8 hearing if prosecutors had met the legal requirement for high blood alcohol content.
Under Virginia law anyone convicted of having a blood alcohol content above 0.15 must serve a mandatory five-day jail term.
Fossella was also convicted of running a red light and ordered to pay a $100 fine.
Fossella was arrested on May 1 in Virginia after he had spent the previous afternoon at the White House, celebrating the New York Giants Super Bowl victory.
While on the witness stand, Fossella insisted he had no more than two or three drinks throughout the course of the evening.
Both Rep. Fossella and his legal team declined to comment because the case is still ongoing.