"Sixth Street has the incredible know-how, experience and bandwidth to devote to the league," NWSL Commissioner Jessica Berman told CNBC.
Waxman, a former Goldman Sachs executive, founded Sixth Street in 2009, and the firm currently has more than $65 billion in assets under management.
This is the company's first foray into women's sports, following investments in Spanish soccer teams Real Madrid and FC Barcelona and the NBA's San Antonio Spurs.
The four former national team players will be represented on the board and will work alongside Sixth Street in setting the team's strategic direction, he said.
Sandberg will partner with the club to create leadership programs that empower women and girls in underserved Bay Area communities.