The striker, who has scored 73 goals for the U.S. and been capped 120 times, joins a club who have won the last 10 French titles.
"I will be immersed in a soccer culture that I believe is precisely what I need at this point in my career," Morgan, who helped the U.S. women win 2012 Olympic gold in London, wrote in The Players Tribune on Tuesday.
"I'm in my prime right now but that isn't going to last forever. I'm not looking to coast.
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"I want to be the best player in the United States and the best player in the world."
(Reporting by Larry Fine in New York; Editing by Toby Davis)
