Kamara, 28, will increase Chris Hughton's striking options.
The forward scored 11 goals in 33 appearances for his MLS club last season and has spells with Columbus Crew, San Jose and Houston Dynamo on his CV.
“I'm delighted to bring Kei to the Football Club, one of Major League Soccer’s best players over the last few seasons," Hughton said.
“There is no doubt it is a big jump to make into the Premier League, but it is an exciting challenge both for him and us here at the Club to prove his talent.
“Kei also adds some valuable competition upfront alongside the current striking options we have here at the Club.”