He served as a radioman with the rank of petty officer third class on board the destroyer USS Stockton, which was based in Queenstown, Ireland, and performed convoy escort and antisubmarine duty.

Following his admission to the bar, he worked in private practice alongside influential Democratic attorney Martin Thomas Conboy Jr.

After returning to private practice for three years as a specialist in criminal law, he served as legal secretary to New York Supreme Court Justice Peter Schmuck, later moving to the chambers of Joseph A. Gavagan in an analogous role.

According to historian Robert Caro, Impelliteri was drafted into his first elected role by Democratic Party leadership, who selected his name from a municipal employee directory.

The party was seeking an Italian American Manhattan resident to bring balance to the citywide ticket and thought an employee in his position would be easy to persuade on political matters.

The Tammany Hall bosses determined that Impellitteri was unsuitable for the role and refused to nominate him as the Democratic candidate for the special election in November 1950; instead, highly regarded New York State Supreme Court Judge Ferdinand Pecora, who was also given the Liberal Party line, ran as the nominee.

"[citation needed] Shortly after Impellitteri's succession, the Kings County District Attorney arrested bookmaker Harry Gross in September 1950 as part of a corruption investigation that caused nearly 500 police officers of all ranks to resign, retire, or be fired.

Impellitteri opposed the corruption, vigorously supporting the Brooklyn District Attorney, Miles McDonald, and firing anyone in his administration associated with former Mayor William O'Dwyer.

[7] Impellitteri is credited with trying to rein in the budget, raising the bus and subway fare to fifteen cents, establishing parking meters on city streets for enhanced revenue, and increasing the sales tax.