She will begin in the role immediately and help the firm expand its digital and social media output.
Peacock was recruited after she contacted O’s managing director via social media.
O founder Kari Owers said: "We're delighted Holly has joined our team to take forward the fast-growing area of the business; social media and digital content strategy."
Peacock said that she has always had one eye on the creative industry in the North East of England, where O is based.
She added: "O PR has always stood out to me, so I’m really excited to be joining."