An Oakland native, Lynch, 34, was a prominent advocate for the city during his 12-year NFL career, primarily with the Seattle Seahawks.
"Growing up in The Town, we always could count on the pro teams in this area but with most of those ones that I grew up with gone, I knew the minute I heard about the opportunity to join Oakland Roots, it wasn't just something I wanted to do, it was something I had to do," Lynch said in a statement.
Lynch initially retired from the NFL after the 2015 season, but he returned to play for the Oakland Raiders in 2017 and 2018, before their move to Las Vegas.
"From the start, we have tried to build an ownership group that was excited about more than just pro sports, but also about Oakland and our Purpose," Roots co-founder and CMO Edreece Arghandiwal said in a statement. "We couldn't be more proud to welcome someone who has long been an inspiration to Oaklanders and all of us at Roots."
The Roots were founded in 2018 and played their first two seasons in the National Independent Soccer Association, the third-tier league of the United States professional soccer system. In September, they announced they would join the USL Championship in the second tier.
Oakland opens the season May 8 at the Phoenix Rising.
Marshawn Lynch explains investment in Oakland Roots SC
Marshawn Lynch joins SportsNation to reveal why he has invested in Oakland Roots Soccer Club.