A statement said his successor will be Inge Plochaet, who is now AB Inbev's vice president, commercial for Western Europe.
She first joined the company in 1995 and will be working alongside MacFarlane "to ensure a smooth transition for the remainder of the year", the statement said.
MacFarlane will take on his new role as zone president for Central and Eastern Europe on January 1, 2012.
He became the leader of the company's UK and Ireland operations in 2008 and has been with the company for 20 years.
MacFarlane said: "It has been a real pleasure to lead the UK team. Our team can be rightly proud of the performance and momentum we have built around Stella Artois, Budweiser and Beck's in the UK. While I'm naturally looking forward to my new role next year, my priority remains to continue working with our customers here and ensuring a smooth transition to my UK successor in the remainder of 2011."