Samsung has been ordered to pay Apple \$1.05bn (£664m) after a court in California found it had infringed patents.
The decision in the complex case came after the nine-member jury began deliberations on Wednesday.
Apple said it may now seek a ban on some Samsung products being sold in the US while Samsung has vowed to appeal the court verdict.
Apple filed its complaint in April 2011 and engaged legions of America’s highest-paid patent lawyers to demand \$2.5bn (£1.6bn) from its top smartphone competitor. Samsung Electronics had fired back with its own lawsuit seeking \$399m.
During closing arguments, Apple lawyer Harold McElhinny claimed Samsung was having a “crisis of design” after the 2007 launch of the iPhone, and executives with the South Korean company were determined to illegally cash in on the success of the revolutionary device.
Samsung’s lawyers countered that it was simply and legally giving consumers what they want: smart phones with big screens.
They said Samsung did not violate any of Apple’s patents and further alleged innovations claimed by Apple were actually created by other companies.
Samsung conceded that Apple makes great products but said it does not have a monopoly on the design of rectangle phones with rounded corners that it claimed it created.
The trial came after each side filed a blizzard of legal motions and ignored advice by US district judge Lucy Koh to settle the dispute out of court.
Samsung has sold 22.7m smartphones and tablets that Apple claimed uses its technology. Mr McElhinny said those devices accounted for \$8.16bn in sales since June 2010.
Apple and Samsung combined account for more than half of global smartphone sales.
As part of its lawsuit, Apple also demanded that Samsung pull its most popular mobile phones and computer tablets from the US market.
From the beginning, legal experts and Wall Street analysts viewed Samsung as the underdog in the case. Apple’s headquarters is a mere 10 miles from the courthouse, and jurors were picked from the heart of Silicon Valley where Apple’s late founder Steve Jobs is a revered technological pioneer.