A federal jury in Texas said Apple Inc must pay about $308.5 million to Personalized Media Communications LLC (PMC) for infringing a patent associated with digital rights management.
The jurors late on Friday directed Apple to pay a running royalty to PMC, which is generally based on the amount of sales of a product or service.
Apple said it was disappointed with the verdict and planned to appeal.
"Cases like this, brought by companies that don't make or sell any products, stifle innovation and ultimately harm consumers," it said in an emailed statement.
PMC, a licensing firm, had originally sued Apple in 2015 alleging the tech giant's iTunes service infringed seven of its patents.
Apple successfully challenged PMC's case at the U.S. patent office, but an appeals court in March last year reversed that decision, paving the way for the trial.
Sugarland, Texas-based PMC has infringement cases pending against companies including Netflix Inc, Alphabet Inc's Google and Amazon.com Inc.