Behan's involvement in the formation of this led to his nomination from the Democratic Party for the Mayor of New Orleans. He won in what is considered a landslide political victory in the 1882 election. He became the first Mayor in the new city charter which was constructed in the post-war process. In 1884, after two years in office, Behan lost his incumbent position in what is considered to be an travesty to the Democratic selection. The popular vote in the election was thrown out and was deemed inconclusive, and the decision was made by a "Ring" of influential politicians. He was then ousted by fellow Democrat J. Valsin Guillotte. Outraged by this decision, Behan left the party and joined the Republican Party. Behan was defeated in his third attempt at Mayor in 1904, and stated that he would never strive to be Mayor of New Orleans for the rest of his life.