[1] After leaving Columbia, Cullen enrolled at the Rensselaer Polytechnic Institute, until his studies were interrupted by the outbreak of the American Civil War.
Cullen became active in Democratic Party politics and served from 1872 to 1875 as an Assistant District Attorney of Kings County.
After the resignation of Alton B. Parker to run for President of the United States in September 1904, Cullen was appointed by Governor Benjamin Barker Odell, Jr. as Chief Judge of the Court of Appeals.
[1] In November 1904, he was elected to a full 14-year term as Chief Judge, nominated as a fusion candidate by Republicans and Democrats.
[1] Cullen was feted at the time of his retirement with a banquet in the grand ballroom of the Waldorf-Astoria Hotel, hosted by the Brooklyn Bar Association and attended by 450 of the most prominent figures in New York political and legal circles, including former Governor and sitting Supreme Court Justice Charles Evans Hughes.
[2] In his speech to the gathering, Cullen expressed pride in the legal profession and offered criticism of President Woodrow Wilson's call for judicial appeal to be "short, sharp, and decisive" so that government could more expeditiously function.
I believe that labor organizations have accomplished great work in behalf of the wage-earners, but to judge how beneficial their rule of the country would be, we have but to recall the crimes committed by many of their members, or if we go further back, to read the history of the Paris Commune in 1871.