The 22-year old striker has joined the Galaxy ahead of the 2014 MLS season but terms of the agreement have not been made public.
Samuel, who has scored 15 goals in 72 outings for Fluminense, follows in the footsteps of fellow countrymen Marcelo Sarvas (who joined from Alajuelense in 2011), Juninho (permanently from Sao Paulo last year after an initial loan) and Leonardo (also from Sao Paulo permanently in 2012 after a loan).
Galaxy head coach Bruce Arena said of Samuel: "We are pleased to add Samuel to our roster.
"Samuel is a young, talented forward with both size and skill. We are confident this addition will help boost our attack in 2014."
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