Fisk was elected President of the London School of Economics Student Union in 1964, then attended the Inns of Court. He was elected as President of the National Union of Students (NUS) in 1968, as a moderate candidate, defeating the then-radical Jack Straw. During his term in office, he toured South Africa, where he supported British academics taking up posts in white-only universities. He launched a campaign for the reform of British universities, but attracted criticism for asking students not to attend protests against the Vietnam War, and opposed removing a "no politics" clause from the NUS constitution. In 1969, he became the first incumbent President of the NUS to lose a bid for re-election until 2016, being defeated by Straw.
After leaving student politics, he worked in the United Kingdom for British Steel Corporation. Fisk emigrated with his family to the United States in 1978, where he was an innovator in the field of healthcare marketing. He first worked for Cooper Medical Center in Camden, New Jersey and then for Thomas Jefferson University Hospital in Philadelphia. He was also an adjunct lecturer at the University of Pennsylvania on Health Care Marketing.
He died suddenly on 14 March 1993 while on a business trip in Orlando Florida.