James will reportedly own an undisclosed amount of shares in FSG and becomes part-owner of other company subsidiaries such as NESN, Roush Fenway Racing, and Fenway Sports Management.
The 36-year-old is accompanied by longtime business partner and friend Maverick Carter as an FSG partner, reports Silverman.
The duo will be the first Black partners in the company's history.
James previously held an approximate 2% share of the Liverpool soccer franchise, which FSG owns.
In addition to James' partnership, FSG approved a $750-million private investment from RedBird Capital Partners, a source told Silverman. The agreement, which is pending approval from Major League Baseball, would make them FSG's third-largest partner.