Dr John Sentamu will be joined at York Minster by friends and family who have been asked to dress formally but with a colourful twist.
In a statement, parents Paul and Alison said: "We are asking as many people as possible to attend and to wear traditional funeral outfits but to add a splash of colour such as a rainbow tie, red shoes, bright hair piece, etc., - whatever you feel comfortable in."
After the dismissal at the end of the service, a private family service of committal will also be held at the Minster.
Katie was found on 9th January with severe lacerations to her neck and chest on a playing field in York. She died later in hospital.
A 15-year-old girl, who cannot be named, has appeared in court charged with Katie's murder. She is due to appear at Leeds Crown Court again on Thursday.