Gastrow became a politician shaped by the liberal politics of 1960s and 1970s South Africa. In 1971, his political views were strengthened by the forced removal of Botshabelo residents to make way for White farmers. This affected Gastrow personally because he had known those affected for some time.
In 1975 he opened his own legal firm and became actively involved in politics as member of the Progressive Party, which later became the Progressive Federal Party (PFP). In 1981 he was elected to represent Durban central in parliament. He quickly rose to prominence within the party political structures and in 1983 he was elected Vice Chairman of the PFP. Dr Van Zyl Slabbert, leader of the PFP, resigned from parliament in 1986 arguing that parliament and parliamentary politics in South Africa had become irrelevant. Gastrow became the National Chairman of the PFP, succeeding Colin Eglin, who had succeeded Slabbert.
Gastrow was instrumental in opening talks between the ANC in exile and the PFP. During the negotiations for the democratic South Africa, Gastrow proposed that the interim government pass a law of amnesty. He supported the view that amnesty be conditional on full disclosure by perpetrators across the political spectrum. It was also his view that such a process, legitimated by a negotiated interim government, could facilitate true reconciliation in South Africa.
Gastrow, S. (1987). Who’s who in South African politics. Vol. II, Johannesburg: Ravan Press