Franz Sigmund Leichter was born in 1930 in Vienna, Austria and emigrated to the United States with his father and brother from German-occupied Paris, France in 1940. Leitcher's mother, Käthe Leichter, was a leading sociologist and feminist who was arrested by Gestapo in 1938, brought to the Ravensbrück concentration camp, and was killed in 1942.

A graduate of Swarthmore College in 1952 for his bachelor's, Leichter served in the U.S. Army in Japan, and then graduated from Harvard Law School in 1957. His first political appointment was to the New York State Assembly as a Democrat in 1968 and continued to be so until 1974, sitting in the 178th, 179th, and 180th New York State Legislatures and representing the Upper West Side of Manhattan. Leichter's most notable efforts during this time was to draft a bill expanding abortion rights, written with Republican Assemblywoman Constance Cook, which passed in 1970, and was the first in the United States to legalize abortion.

In 1974, Leichter won election to the New York State Senate in the Democratic primary and would remain in the Senate until 1998; sitting in the 181st to 192nd New York State Legislatures, again representing the Upper West Side. During his time in the Senate, Leichter would fight for moral and ethical reform, focusing on New York City's banking and real estate industries and criticizing the leadership of the Democratic and Republican parties. Most of his efforts surrounded improving living conditions, from canine waste laws to protecting tenants from unsanitary or dangerous living conditions and establishing parks and green spaces along the Hudson River. He served as Director of the Hudson Rover Park Trust Board, which constructed a park along the Hudson in Manhattan. Leichter was also an advocate for consumer rights, drafting legislation that required banks to directly credit checks to accounts instead of holding the funds for their own purposes as well as releasing Consumer's Guides to Banks and Consumer's Guide to Credit Cards, which called attention to hidden charges and fees that the average consumer may not be aware of.

Most notably, in 1990 Leichter drafted the first state bill in the United States to expand civil rights to include domestic partnerships, which did not pass but did lay fundamental groundwork for the LGBTQA+ community. This bill is credited with creating the foundation of the passing of the New York State same-sex marriage bill in 2011.

In 2000, Leichter was nominated as a Director of the Federal Housing Finance Board (FHFB) by President Bill Clinton. He was re-nominated by President George W. Bush, serving until his term expired in 2006. In 2009, New York State Governor David Paterson nominated Leichter to serve on the State's Banking Board, which was confirmed by the State Senate. He would serve there until 2011, when the board was eliminated.

In addition to his political career, Leichter was also a practicing attorney for 50 years. He specialized in commercial litigation and in representing foreign clients.

Leichter died in June 2023 and was survived by his children Kathy and Josh and six grandchildren. He was predeceased by his first wife Nina Williams and his second wife Melody Anderson.