In 1949, he completed a clerkship with New York State Court of Appeals Judge Stanley H. Fuld before opening his own law practice in Manhattan a year later—"in part because anti-Semitism at the time made finding work at a firm difficult.

[9] As a federal judge, he worked with a number of mass tort cases, including those relating to Agent Orange, asbestos, tobacco, breast implants, diethylstilbestrol, Zyprexa, and handguns.

He has been known to take on large numbers of cases from other judges, and on one occasion collected most of the unresolved habeas corpus petitions in the Eastern District to bring finality to the claims of many prisoners.

[8] His change to inactive senior status meant that while he remained a federal judge, he no longer heard cases or participated in the business of the court.

[11] Following two years in private practice, Weinstein was appointed to a tenured professorship at Columbia Law School from 1952 (becoming a full professor in 1956) until commencing his judicial service in 1967.

[13] The Second Circuit Appeals court reversed Weinstein's ruling in favor of the City of New York (Mayor Michael Bloomberg) against a group of gun manufacturers.

"[15] In March 2005, Weinstein dismissed a lawsuit filed by the Vietnamese victims of Agent Orange against producers of chemicals defoliants/herbicides on the grounds that use of the herbicide in warfare had been legal under the international law of the time.

[21] In December 2017, Weinstein sentenced three gang members to up to eight years in prison for robbing at gunpoint a family and their five young children inside their home.

[22] On June 11, 2018, Weinstein explicitly criticized recent Supreme Court precedent when he refused to grant qualified immunity to police officers who had allegedly beaten a resident when he tried to stop them from entering his home without a warrant.