Gerken is pursuing other business opportunities, according to a statement, but he will retain his role as chairman of the sister wholesaling business WaverleyTBS.
Porter's title will be off-trade sales director and will start his new role on April 6. He will report to Stefan Orlowski, Heineken UK managing director and become a member of the Heineken UK senior management team.
Orlowski said: “I would like to welcome Martin to Heineken UK. He will certainly be joining us at a time of huge opportunity and challenge within the industry and we welcome the fresh insight and experience that he will bring.
“I would also like to offer my personal thanks to Mark, both for the significant contribution he has made to the business over the last 21 years and for the support he has given me since I joined Heineken UK.”