Marcantonio was elected to represent New York's 20th Congressional District in 1934 as a Republican in the Fiorella LaGuardia mould; he moved to the American Labor Party ticket in 1938 and was elected for a further six terms.
Marcantonio was a true progressive who always voted in the best interests of working people (he was a tireless defender of the pro-labour Wagner Act and opponent of the 'pro-slavery' Taft-Hartley Act), whilst also being a vocal supporter of civil rights legislation decades before it was politically feasible. Though it's easy to consider him as a patsy for the Communist Party, Marconantonio fought tooth and nail against blacklisting and HUAC.
We live in a time when very few left-wing politicians are willing to stand on principle. Alan Grayson and Dennis Kucinich are our two current heroes in the House, but whenever I listen to them, I think of Vito Marcantonio. If you've never read his book, I Vote My Conscience, there are plenty of second-hand copies available online for a dollar or two.