The 29-year-old was captured by RSL as a Designated Player earlier this month following a stint with Argentina's biggest club - Boca Juniors.
Martinez has revealed he always planned to make his way to the USA and is now looking forward to being a part of the burgeoning competition.
"After I ended my contract with Boca, I was a little anxious," Martinez said at his unveiling on Monday.
"But I had many options. I'm happy with this decision because I always wanted to play here in this country, in this league and I didn't know in what year, in this moment or before, but I'm happy to be here.
"The league is growing up very fast, and I want to play here. It was an easy decision to make."