Born in Quincy, Massachusetts,[1] Gaziano received his Bachelor of Arts from Lafayette College in 1986 and his Juris Doctor from Suffolk University Law School in 1989.

In 2001, he was appointed the First Assistant United States Attorney for the District of Massachusetts, where he was a member of the Organized Crime Strike Force.

In April 2020, Gaziano wrote for the unanimous court when it found that warrantless use of automatic number-plate recognition cameras to surveil a suspected heroin distributor's bridge crossings to Cape Cod was not an unconstitutional search because of the limited time and scope of the observations.

[4][5] In February 2022, the Supreme Judicial Court ruled that a criminal defendant lacked a reasonable expectation of privacy in a Snapchat story he shared with an undercover Boston police officer, who friended the defendant using a pseudonym and then used the clip to charge him in an illegal gun case.

Writing for the court, Gaziano said that requiring police officers to always identify themselves would render "virtually all undercover work" unconstitutional.