The contents of the note were not revealed.
Authorities say there were no suspicious circumstances in the death and no malice is suspected. Coroner's officer Lynda Martindill said the 40-year-old designer died from asphyxiation and hanging.
McQueen's mother died just days earlier, and the designer had left several messages on Twitter expressing his grief. He described an "awful week" and said he had to "somehow pull myself together and finish."
His Twitter account has since been deleted.