Manzi was born in Manchester, New Hampshire to a single mother of Italian descent.
[1] He graduated from the College of the Holy Cross and obtained a master's degree from the Yale School of Drama.
Manzi wrote Perfect Crime in 1980 at age 25, while an understudy for a role in Amadeus on Broadway.
[2] Early reviews of Perfect Crime described it as confusing, and Manzi continually rewrote the play throughout the rest of his life.
[3] As an actor, Manzi appeared in the films The Manhattan Project (1986) and Nuts (1987).