Mrs Okonjo-Iweala served under President Olusegun Obasanjo from 2003 to 2006 and President Goodluck Jonathan from 2011 to 2015.

She tweeted the news of her appointment, saying she was "excited" to work on a platform that connects people and ideas.

Ngozi Okonjo-Iweala?@NOIweala

 Excited to work with @Jack and an incredible team on the Board of Twitter, a global platform that is such a strong connector of people and ideas.

3:53 PM - Jul 19, 2018

Twitter, like other Silicon Valley companies, has been criticised for not being inclusive enough. With Mrs Okonjo-Iweala's appointment, Twitter's 10-member board now has three women, two of whom are black.