The 22-year-old forward saw time for Fluminense during the previous two seasons, scoring four Serie A goals in the most recent campaign and five in the Rio club's championship-winning 2012 campaign. He also featured for the club in the Copa do Brazil and the Carioca.
"Samuel is a young, talented forward with both size and skill. We are confident his addition will help boost our attack in 2014," Galaxy coach Bruce Arena said in a news release.
The new signing could help fill the void left by Jose Villarreal, a 20-year-old homegrown Galaxy player currently on loan with Liga MX side Cruz Azul.
Terms of the loan agreement were not announced by the team, per club and league policy.