Facebook said COO Sheryl Sandberg is joining the company’s board, making her the first female board member for the social network.

Sandberg, who joined Facebook in 2008 to create a business model for the young company, was described by CEO Mark Zuckerberg in a statement as his “partner” and essential to the company’s “growth and success.” “Her understanding of our mission and long-term opportunity, and her experience both at Facebook and on public company boards makes her a natural fit for our board,” said Zuckerberg.

Facebook has come under fire from corporate governance advocates over having no women on the board.