Both MacKenzie and Elisabeth Lewis-Jones, the CEO of the agency, sent PRWeek an agreed joint statement which read: "Jason MacKenzie has left Liquid today, 12 December, after nearly six years as managing director, in order to pursue other opportunities and projects.
"The directors wish him well for the future and his forthcoming role as president of the Chartered Institute of Public Relations."
MacKenzie becomes president of the CIPR on 1 January, having been elected unopposed in late 2015. The CIPR elects its presidents a year ahead of them taking office - Sarah Hall, who operates as Sarah Hall Consulting and is the editor of #FuturePRoof, will be the president in 2018 after her recent electoral victory.
However, it is not known whether MacKenzie has another full-time role or project to go to after leaving Liquid.
Founded in 2004 by Lewis-Jones, Liquid has offices in Birmingham, Guernsey and Jersey and ranked 143rd in the PRWeek UK Top 150 2016. Specialisms of the firm include financial services, education and b2b.
A former journalist, MacKenzie joined Liquid in February 2011 when it bought One Strategic, the Guernsey and Jersey agency he co-founded. He also lectures at Birmingham City University.