They replace chairman Tanya Joseph, director of business partnerships at Sport England, and vice-chairman Robert Phillips, co-founder of Jericho Chambers, who have led the group since its launch in 2013.
The Diversity Network aims to promote more opportunities in the sector for people from different backgrounds.
Over the past two years, it has developed initiatives such as the joint PRCA/PRWeek scheme PR Internships For All, the PRCA’s PR Careers Guide and schools outreach programme, and the CMS Diversity Module.
Reeves, who works with a range of clients at John Doe including Beats by Dr Dre, Absolut and W Hotels, previously worked with Cooper at JCPR.
He said: "Clearly this is an issue with which I have personal experience, and it is such a shame that there is still a need for this in 2015 – but there is. I am excited to explore this with my old boss who taught me professional self-value and what it means to work for someone that hires based on ability and talent rather than what school you went to, or whether you look like them.
"I hope to offer a healthy mixture of carrot and stick to get action on diversity.’’
Cooper, who co-founded JCPR in 1987 before the business was acquired by Edelman in 2004, said: "Given that our role in the communications world is to reach out and engage with the human race, it is imperative that our industry reflects that diversity and represents opportunities equally and fairly.
"I am delighted to reunite with Rana in this mission and I look forward to enjoying again our magical mix of provoking thought and driving action."
The PRWeek/PRCA Census 2013 demonstrated the industry’s failure to become truly inclusive: 91 per cent of people within in it are white, a fractional improvement on the previous 2011 Census, when white people accounted for 92 per cent of the business.