He told PRWeek the departure was "amicable" and that he's seeking a new challenge, details of which are expected in January.
Medley left Nexus in November, having joined as managing director in February 2012 from Spider PR, where he was also MD. Before Spider PR he was MD of Publicis Consultants, following senior stints at GCI and Porter Novelli. He has worked in agency PR for more than 20 years.
Nexus, which is based in London, confirmed that Medley had left the company and that his successor had not been appointed.
Independently owned Nexus specialises in the food, drink, healthcare and wellbeing sectors. It was listed at number 74 in PRWeek’s most recent Top 150 list of UK PR agencies by size, with UK fee income of £2.8m in 2014.