Devine was UK CEO of corporate and public affairs specialist Newgate, as well as chief operating officer at Porta, its parent company and also owner of Publicasity, Redleaf and others. He confirmed to PRWeek that he had left these roles at the end of February.
He had joined the company in mid-2016 from its larger rival MHP, after 12 years with it and its forerunner Mandate.
Devine's appointment to Porta was made by new group MD Steffan Williams, who had arrived in September 2015.
Developments at the group since Devine's arrival have included the retirement of executive chair David Wright and the promotion of Williams to CEO, as well as the £3m purchase of a 19.3 per cent stake in Porta by Italian group SEC. Newgate itself integrated the old PPS business into its operation, giving it a total of 90 staff.
Devine has registered Park Street Partners as a business at Companies House, through which he will advise a number of clients, but has no immediate plans to hire staff or build an agency.
He told PRWeek: "[My departure] was entirely amicable - there have been a lot of changes to my role and the group as a whole and it seemed like the right time to move on. I'm excited for what's next."
Start-up in Shanghai
The agency has also opened a new office in Shanghai, which will be set up by Grace Zhang, a partner of the agency in Hong Kong.
She will report to Newgate China managing partner and founder Richard Barton. Both joined the firm in 2013.
The new office means it has more bases in APAC than in the UK: in addition to several offices in its home market, Newgate also has bases in Abu Dhabi, Singapore and four in Australia. The head of Newgate Australia joined Porta's board as an executive director in November last year.
Porta said in a trading statement in January, ahead of April's release of 2017 results, that adjusted EBITDA should be around £2.5m; ahead of the result achieved in 2016 due to a Brexit-related dip, but still slightly below 2015's headline EBITDA figure.