The 24-year old originally joined the Galaxy on loan in 2010 and has since emerged as a key player with the Los Angeles club, helping them to back-to-back MLS Cups in 2011 and 2012.
Galaxy head coach Bruce Arena suggested in an interview with beIN Sports that the signature of Juninho had already been required for the 2013 campaign following the departure of David Beckham and hinted that a Designated Player was also on the cards.
"That was inevitable and we were fully prepared for the day he leaves," Arena said of Beckham's exit.
"And we've been fortunate we've been able to re-sign Juninho, so we'll have him back and (Marcelo) Sarvas and (Mike) Magee back in the midfield. And we need to get another player there and we're working on it, as well, and there's a chance we'll get a designated player that can slip into midfield, as well."