She is also a mentor to Georgina Cotton, a communications specialist at Cabinet Office, in this year's PRWeek and Women in PR mentoring scheme.
At O2, Green leads an integrated communications function, including PR, corporate and strategic communications, internal communications, public affairs and social media. As a member of the executive team, she will offer her communications counsel and experience at the highest level of the company.
Mark Evans, Telefónica UK’s Chief Executive Officer, said: "I am delighted to welcome Nicola to the executive team. During her time at O2, Nicola has made a substantial contribution to O2’s business strategy, providing senior strategic counsel and demonstrating an unrelenting commitment to our customers, employees and culture.
"I am excited by the contribution Nicola will make to our team as we strive to make every day better for our customers."
Green added: "I am incredibly proud that corporate affairs is now represented at the top table at O2. I've spent my career campaigning on the value corporate affairs brings to significant decision-making in organisations, and I’m thrilled to be putting this into practice.
"This is a fascinating time for businesses in Britain and in particular the mobile industry. I'm looking forward to working with the executive team to improve the lives of our customers and employees through communications."
Green joined O2 in March 2003 and has been instrumental in establishing O2 in the UK.
The telco said her notable projects include bringing the iPhone to the UK and launching O2’s custom plans.
Prior to O2, Green worked at Orange, where she led on consumer PR and developed their sponsorship properties at BAFTA and Glastonbury Festival.
She has also worked as a brand manager at Dr Pepper, and oversaw a number of FMCG brands at communications firm Burson-Marsteller.