The 22-year old midfielder was taken in the third round of the January draft, with pick number 57 overall, and has impressed enough during preseason training to win a MLS contract.
Martinez will occupy one of three available supplemental roster spots with the 2014 MLS Cup winners and is thrilled to have finally made it into a professional soccer environment.
"I feel so blessed to have the opportunity to play for the best team in MLS," Martinez said in a club statement.
"I have worked for this my whole life. Since I was three or four years old, I have wanted to play professional soccer. Now that it's happened, I want to make the most of the opportunity."
The Uruguay-born Martinez, who starred for North Carolina State in college and spent time with PDL side Carolina Dynamo in 2013, appeared in seven of 10 preseason matches for Sporting this year, providing three assists.
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