The record companies involved in the lawsuit are Sony BMG, Arista Records LLC, Interscope Records, UMG Recordings Inc., Capitol Records Inc. and Warner Bros. Records Inc.
The record companies had alleged Thomas had shared 1,702 songs online, in violation of their copyrights.
The case against Thomas went to court after she rejected an offer from the recording companies to pay a few thousand dollars in fines.
In the first law suit of its kind to go to trial, the companies accused Thomas of downloading music files without permission and offering them online through Kazaa, a file-sharing account.
Record companies have filed about 26,000 lawsuits since 2003 over file-sharing, which has affected sales because it allows people to get music for free instead of paying for recordings.
Other defendants have settled cases by paying the companies a few thousand dollars.
The Recording Industry Association of America (RIAA), which co-ordinates lawsuits against those who illegally download copyrighted music, says the number of households using file-sharing programs to download music has risen in recent years.
In April 2003, the number of file-sharing program users stood at 6.9 million monthly, before the lawsuits began, rising to 7.8 million in March 2007.
During the three-day trial, the record companies presented evidence they said showed the copyrighted songs were offered by a Kazaa user under the name "tereastarr".
Their witnesses, including officials from an internet provider and a security company, testified that the internet address used by "tereastarr" belonged to Thomas.
Toder said in his closing statement that the companies had failed to prove that "Jammie Thomas, a human being, got on her keyboard and sent out these things."
Thomas says she was wrongfully targeted by SafeNet, a contractor employed by the recording industry to patrol the internet for copyrighted material.
Gabriel said Thomas' defence had used "misdirection, red herrings [and] smoke and mirrors," and told jurors that a verdict against Thomas would send a message to others who downloaded copyrighted files illegally.
"I only ask that you consider that the need for deterrence here is great," he said.
Before the verdict, Cary Sherman, president of the RIAA, said he was surprised it had taken so long for one of the industry's lawsuits against individual downloaders to come to trial.
Illegal downloads have "become business as usual, nobody really thinks about it," Sherman said.
"This case has put it back in the news. Win or lose, people will understand that we are out there trying to protect our rights."