A Sydney man charged with kidnapping and sexually assaulting a Japanese tourist has died before he could stand trial.

Robert Mariage, 49, allegedly took the woman to his home at Miranda in April last year, where he handcuffed and repeatedly sexually assaulted her.

The 29-year-old woman reported the alleged attack to police after Mariage let her go.

He was charged with three counts of aggravated sexual assault while inflicting actual bodily harm and one count of kidnapping.

Mariage was due to stand trial in the District Court in Sydney this month, but it has since emerged that he had died.

The circumstances surrounding his death are unknown, but he is believed to have been on bail at the time.