She endorsed Bill de Blasio in the 2013 New York City mayoral election, who went on to win the Democratic nomination and the general election. Nixon campaigned actively for de Blasio, whom she had worked with since the early 2000s when campaigning against Michael Bloomberg's education policies. De Blasio credited Nixon and union leader George Gresham as the two "architects of (his) campaign" in the Democratic primaries, when he defeated the favorite Christine Quinn. After his election, de Blasio appointed Nixon as his representative to The Public Theater.
