Actress Cynthia Nixon is expanding her working relationship with New York Mayor Bill de Blasio by joining an advisory board.

The Sex and the City star, who was an early supporter of the politician, has signed up for the Mayor's Fund to Advance New York City, a non-profit organisation which raises money from private investors for public programs.

Nixon was previously appointed to De Blasio's transition committee to help the Democrat fill key positions in his administration and advise him on policy ideas at the start of his tenure in January (14).

Her wife, Christine Marinoni, is also working with the Mayor, serves as a special adviser for community partnerships in the Department of Education.