Born in Wellington, New Zealand, Forrester became a deck boy on a merchant ship at twelve years old taking with him only a seaman’s bag containing socks, sketch paper and pencils. At fifteen he sold his first picture asking the buyer to return the frame, enabling him to use it for another painting. At the beginning of the Second World War, Forrester voluntarily enlisted in the New Zealand army and fought in the Pacific Ocean and North Africa. After the war he returned to New Zealand, where his first exhibition was held in Auckland in 1946.
He moved to England in 1953, working at St. Ives for some time where he became a member of the Penwith Society. In 1955 an exhibition of his work was held at Gimpel Fils, London. Forrester moved to Paris in 1960 with his wife, whom he divorced in 1963 soon after his daughter was born. The artist remarried and worked in Paris for several successful years before taking the ‘Grand Tour’ of Italy, studying the great painters of the Middle Ages and of the Renaissance, staying for some time in Tuscany. In 1973 he travelled to Calice Ligure (Italy) and decided to make it his home, essentially removing himself from the outside art world; shows, press conferences and interviews.
A memorial exhibition of his work was held at Finale Ligure in 2003.