Schwarz rose from the childhood poverty he experienced as a German-Jewish refugee to become a lawyer and a member of the Transvaal Provincial Council, where from 1963 to 1974, he was Leader of the Opposition. In the 1964 Rivonia Trial he was a defence lawyer. Advocating a more aggressive political opposition to the National Party's racial policies in the 1960s and 1970s, as Leader of the United Party in Transvaal and leader of the liberal "Young Turks", he clashed with the United Party establishment. He pioneered the call in white politics for a negotiated end to apartheid and in 1974 signed the Mahlabatini Declaration of Faith with Mangosuthu Buthelezi for a non-racial democratic society in South Africa. He was in the opposition for over 40 years and was a founding member of the Democratic Party. In light of his record, his appointment as South African Ambassador to the United States in 1990 was widely heralded as symbolic of the government's commitment to ending apartheid, and played a significant role in renewing the nation's image as the new democratic South Africa.