[3] Finnigan studied law under Anthony Barrett, and at the age of 51 was admitted to the Bar.
He was the first lawyer in the state to be admitted to practice as an official examiner of titles under the Torrens system.
He also was the confidant and personal lawyer of Hugh McLaughlin, who secured him his first political position as official searcher.
[2] In 1892, Finnigan was elected to the New York State Assembly as a Democrat, representing the Kings County 17th District.
[2] From 1898 to 1902, he served as Assistant Corporation Counsel,[2] in charge of the Bureau of Street Openings.