Terms of the deal were not disclosed for the 34-year-old center back, who has been without a club for nearly two years.
“Oguchi is a big, physical presence who brings experience and veteran professionalism, important traits that we believe will be an asset for our group of young defenders,” Philadelphia Union sporting director Earnie Stewart said in a press release. “He provides excellent depth at the centerback position and we are pleased that we were able to add him to our squad.”
Onyewu last played for Charlton Athletic in the English Championship in February 2015, meaning it will have been two full years since his last professional match by the time the Union kick off their season on March 5.
The big defender has spent the entirety of his career in Europe following two years at Clemson. Much of that time was spent with Standard Liege in Belgium, where he played from 2004-09, with a brief loan at Newcastle United mixed in during that span. Onyewu spent time with AC Milan from 2009-11, though only played in one Champions League contest with the club. He also had stints at Metz, La Louiviere, Twente, Sporting CP, Malaga, Queens Park Rangers and Sheffield Wednesday.
The Maryland native has been capped 69 times for the United States and appeared for the national team at both the 2006 and 2010 World Cups. His last appearance for the national team came in March 2014 against Ukraine.