Executive producer Bob Daily previously revealed that the team behind the drama had discussed hiring the Ugly Betty star but insisted that the negotiations had not gone further than that.
However, Cherry has now told TV Guide Magazine that Williams will appear in the programme as a series regular.
He said: "I'm a big fan of Vanessa's work and I'm so excited that she'll be moving into the neighbourhood next season to cause trouble in all the ladies' lives."
Cherry added that Williams's character will not be the centre of next season's mystery, explaining that it will focus instead on the show's returning character.
Desperate Housewives continues in the UK tonight at 10pm on Channel 4.