MacKenzie, who is the CIPR president for 2017, spent nearly six years as MD of Birmingham-headquartered Liquid before leaving in December on the eve of taking up the presidency.
A former journalist, he had joined Liquid when it bought One Strategic, the Guernsey and Jersey agency he co-founded.
Mackenzie now takes the role of head of Bottle Bournemouth and will work alongside publisher Lauren Whitty, who joins next month and is currently a senior account executive at Saltwater Stone in neighbouring Poole. Further recruits are expected, including from graduates of Bournemouth University's renowned PR school.
Natasha Hill, managing director at Bottle, said of the launch: "Bournemouth may not have been the obvious choice when looking to expand, but it really stood out against other candidate cities. There is a growing creative and digital economy in Bournemouth, with a welcoming bunch of innovative agencies, who are proving you don’t need to be in London to create great work.
"We immediately felt a connection and are very excited to have found Jason and Lauren to start this exciting chapter in a very cool and highly relevant Echo Building."
With revenue just shy of £2m and 24 staff in 2016, Bottle ranks as the UK's 122nd largest agency in the 2017 PRWeek UK Top 150. Recent clients have included the Dallaglio Foundations, insurer AXA PPP Healthcare and tyre-maker Goodyear.