Mr. Mueller, 55, originally sued the pop star for $3m (£2.3m), saying she cost him his job.
His claim was dismissed on Friday in a Denver court.
US District Judge William Martinez ruled that Ms Swift was not liable, as Mr Mueller had not proved she set out to get him fired.
The DJ made the same claims against the singer’s mother Andrea Swift, and her radio liaison, Frank Bell. A jury will now decide if they are accountable for Mr Mueller’s sacking.
Ms. Swift, 27, has countersued the DJ for allegedly groping her after she agreed to pose for a photo with him and his girlfriend.
She is seeking a symbolic $1 in damages, which she has pledged to donate to charity.
The ruling against Mr. Mueller came on the fifth day of the trial.
Ms. Swift’s ex-bodyguard gave evidence on Friday, backing her sex assault claims by testifying that he saw the DJ reach under her skirt.
Greg Dent told the Colorado court he “did not see his hand touch her physically”, but “saw his hand under her skirt”.
The alleged assault is said to have occurred in 2013 during a Denver stopover on the singer’s Red tour.
Mr. Mueller, then a host on the radio station KYGO, had been invited to meet her before the show.
Ms. Swift complained to KYGO and the station fired Mr Mueller two days later.
Mr. Dent, who no longer works for Ms Swift, told the court he was steps away when Mr Mueller posed with his girlfriend and the pop star.
“She reacted, pushed her skirt down and moved over closer to [Mr Mueller’s girlfriend]. So in my opinion, I knew he touched her,” he said.