The 31-year-old right-sided winger has compiled 13 caps for Sweden, appearing most recently for his country in January 2012. Ishizaki spent the past eight seasons with Elfsborg in the Swedish top flight, winning a pair of league titles.
"Stefan is an excellent addition to our team," said Galaxy coach Bruce Arena in a news release. "He is an experienced player, an exceptional passer and a proven winner."
With newcomers Samuel and Rob Friend vying for playing time alongside Robbie Keane up top and Landon Donovan likely occupying one flank, Ishizaki figures to compete with the likes of Robbie Rogers and Gyasi Zardes for minutes on the opposide side.