Hailing from Glasgow, Scotland, Forrester began his writing career on such English television series as Ivanhoe, The Adventures of William Tell, Sir Francis Drake, Orlando and The Saint. Between 1959 and 1961, he wrote seven episodes of the British series Interpol Calling, and between 1960 and 1964, he wrote ten episodes of No Hiding Place. Perhaps most notably, Forrester wrote ten episodes of Fantasy Island, the hit ABC series starring Ricardo Montalban and Wendy Schaal. Among the episodes he wrote were: