Along with Christopher Magee (1848–1901), his political partner, the two ran the Republican Party machine that controlled the city for the final twenty years of the 19th century.

The family emigrated later that year to the United States and settled in Pittsburgh's Sixth Ward, famous for its hard-scrabble politics, where his father established a small contracting business.

Educated in the Pittsburgh Public Schools, Flinn dropped out at age 9 to deliver newspapers, shine shoes, and later apprentice in the gas and steam fitting trades.

In 1877, he was elected to the State House to represent the Pittsburgh area by holding one of Allegheny County's allotted at-large seats.

In 1882, Flinn was appointed chairman of the executive committee of the Pittsburgh Republican party, a position he held for the next 20 years, and in 1890 he was elected to the Pennsylvania State Senate, where he sponsored the Good Roads Act, which became law in 1895.

Penrose, who had previously served as state committee chairman himself from 1903 through 1905, did not attend the convention, and did not seek re-elected to the post of Republican National Committeeman.

As a result of politics and a "lowest responsible bidder" scheme, Booth & Flinn won most large construction and paving contracts in Pittsburgh and Western Pennsylvania, where they built streets, trolley lines, and bridges, usually amid charges by competitors of graft.

Flinn's political and business organization began to crumble in the late 1890s when a flap over the rigged bidding system came to a head with Edward Manning Bigelow, director of public works.

Flinn withdrew from local politics, as a result, and retired to a country estate north of the city called Beechwood Farm.