Under the provisions of the New York Constitution of 1938, re-apportioned in 1953, 58 Senators and 150 assemblymen were elected in single-seat districts for two-year terms.

[1] On February 4, 1964, Constance Baker Motley, a lawyer of Manhattan, was elected to the State Senate, to fill a vacancy.

The Legislature met for the first regular session (the 186th) at the State Capitol in Albany on January 9, 1963;[2] and adjourned on April 6.

The Legislature met for the second regular session (the 187th) at the State Capitol in Albany on January 8, 1964;[4] and adjourned on March 27.

In 1964, the U.S. Supreme Court handed down several decisions establishing that State legislatures should follow the One man, one vote rule to apportion their election districts.

Senators John H. Hughes and Lawrence M. Rulison (both Rep.) questioned the authority of the federal court to shorten the term of the 1964 electees,[8] alleging excessive costs for the additional election in an off-year.

Guy James Mangano, Edward S. Lentol and Jeremiah J. Moriarty changed from the Assembly to the Senate at the beginning of this Legislature.