Werribee Mercy Hospital opened on 4 January, 1994 with just 70 staff.  Since then the hospital has treated over half a million patients and now employs over 900 staff. The hospital has grown to meet the demands of the area's ever increasing population. In the first six months the hospital delivered just 20 babies, it now delivers around 1,750 babies each year.
During its first year of operation the hospital treated 6,991 inpatients, in 2005 this figure exceeded 20,000. In 1994 the average length of stay was 1.94 days, it is now over 2.5 days and 13 days for mental health inpatients.  This reflects the hospital's increasing capacity to treat more severe cases that require longer hospital stays. 

A purpose built residential mental health unit was opened in 1997.  Since then the Mental Health Program has grown to include community management and rehabilitation programs, support for General Practitioners and Community Health centres and even help for the homeless who are mentally ill.

In April 2004 the State Minister for Health Bronwyn Pike visted the hospital to officially announce the start of a $10 million expansion and upgrade, which was completed on time and on budget in mid 2005.

Major milestones include:

1991	State government invited the Sisters of Mercy to operate a new hospital in South West Melbourne.
1992	Construction of the new hospital started on a green field site in Werribee.
Jan 1994	Mercy staff move into the newly completed hospital and admit first patient.
1996	Third operating theatre opened.
1997	Opened a purpose-built mental health unit providing residential/community mental health services.
May 2003	Opened 12 cot Special Care Nursery and a Day Procedure Unit.
Sept 2003	Opened residential Mother Baby Unit for mothers with mental illness.
Nov 2005	Completed a $10 million upgrade of the hospital, including a 12 bed Pallitive care Centre, additional operating theatre and new Emergency Department.