Born in 1924 in Chicago to non-religious Jewish parents, Leonard W. Schroeter grew up in Hammond, Indiana, and attended Indiana University from 1942 to 1943. While in the United States Army from July 1945 to January 1946, he wrote for and served in Florence in the Allied Area Command. After his army service he attended the University of Chicago’s graduate school in the Division of International Relations, where his studies focused on the Soviet Union. He received his M.A. degree in 1949. From 1948 to 1951 he attended Harvard University Law School, from which he received a J.D. degree. He also taught constitutional history for two years at Northeastern University and directed its Center for International Relations. In June 1951 Schoeter joined the legal staff of the National Association for the Advancement of Colored People’s Legal Defense & Education Fund (NAACP-LDEF), headed by Thurgood Marshall in New York City. The LDEF team prepared the school segregation cases which eventuated in the Brown v. Board of Education decision by the U.S. Supreme Court in 1954.

At the end of 1952 Schroeter moved to Seattle to become Northwest director of the Anti-Defamation League of B’nai B’rith. Along with this position he became active in civil rights and civil liberties groups, including the American Civil Liberties Union, to which he had belonged since 1946. He became a board member of the ACLU of Washington in 1953 and in 1964 became the first national board member from the Pacific Northwest. When the civil rights movement arose in 1963-1964, he became active in the Lawyers Constitutional Defense Committee (LCDC), a loose federation of groups which represented blacks arrested in civil rights demonstrations in Southern states. In this connection he traveled to Mississippi and other Southern states in 1965.

From 1955 to 1956 Schroeter served as deputy prosecuting attorney for King County. At the request of Seattle mayor Allan Pomeroy, Schroeter was appointed to the Mayor's Advisory Committee on Police Practices in 1955 to investigate a large number of instances of alleged police brutality. In 1956 he left the prosecutor's office and started a largely plaintiff trial practice which grew and became the firm Schroeter, Goldmark & Bender in 1968. He developed a national reputation as a plaintiff’s trial lawyer and as an advocate for constitutional rights.

From 1970 to mid-1972 Schroeter lived in Israel, serving as principal legal assistant to the attorney general of Israel. His major assignment was to mobilize world opinion to the human rights of Jews who were prohibited from leaving the Soviet Union. He made a clandestine visit to the USSR in August 1972, where he met with dissident Soviet writers, including Andre Sakarov, and with Jews striving to leave the USSR. This visit accelerated his involvement in their causes. After returning to the U.S. in September 1972 he tried, but failed, to interest the Nixon administration in these human rights causes. Schroeter then turned to his senator, Henry M. Jackson of Washington State, who adopted them. The Trade Act of 1974, commonly known as the Jackson-Vanik amendment, was the result. This law made non-market economy countries that denied their citizens the right to emigrate ineligible for normal trade relations with the U.S.

As Soviet Jews began to emigrate to Israel, Schroeter aided them and became the attorney and representative of many Soviet samizdat writers and human rights activists. From 1973 to 1981 he was the attorney and underground contact for samizdat writers who wanted to get their writings published in the West, serving as their representative to publishing houses in Europe and the U.S.

Schroeter drew upon his background and experiences to write a book, , which describes the Soviet Jewish dissident movement. It was published in 1974 and reprinted in 1979. Schroeter continued to practice law until August 1989 and was active in a variety of constitutional, civil rights, and human rights causes. His major effort after 1994 was the issue of access to justice.