The jury in the state of California awarded Apple more than a billion dollars in damages in its decision Friday.
Samsung is likely to appeal the verdict, which said the South Korean company had illegally used several Apple technologies.
Apple also claimed that Samsung illegally copied the shapes of its popular iPhone and iPad devices and used them to create its own line of Galaxy devices.
Samsung had argued that by 2006 - months before Apple introduced its first iPhone in early 2007 - it was developing a next generation of smartphones with a rounded rectangular body that both companies now use.
The case is part of a multibillion-dollar global legal battle between the two technology powerhouses. Industry analysts say the smartphone market is valued at more than $200 billion.
Earlier Friday, a South Korean court ruled that both Apple and Samsung infringed on the others' patents.
The Seoul court said that Apple infringed on two Samsung wireless patents, while Samsung violated one of Apple's design patents. It awarded small damages to each side and imposed a limited ban on the sale of each company's products in South Korea.
Some information for this report was provided by AP, AFP and Reuters.