MGen Downes joined the Canadian Forces in 1989 as a medical student at the University of Manitoba. After completing a residency in Family Medicine in 1994, he was posted to Petawawa where he served two years with the Royal Canadian Dragoons, followed by a year posting with 2 Field Ambulance. He was then posted to Winnipeg, as a flight surgeon and diving medical officer, and in 1999, he was promoted to become the 17 Wing Surgeon.
In 2001, he moved across the base to 1 Canadian Air Division Headquarters, where he served 3 years as the Aerospace Medical Programs Flight Surgeon.
In 2004, he was posted to San Antonio, Texas to undertake a two year Residency in Aerospace Medicine at the US Air Force School of Aerospace Medicine. This included a Master of Public Health degree from the University of Texas. On completion of the program, he was promoted to Lieutenant Colonel and he assumed the role of LFCA/JTFC Surgeon, in Toronto.
In 2009, he moved to Ottawa where he served for a year as the CEFCOM/Canada COM/CANOSCOM Surgeon. In 2010, he was posted to the Canadian Forces Language School at Centre Asticou for second language training, which he completed in 2011. On 01 January 2012, he was promoted to Colonel and assumed the role of RCAF Surgeon. In 2014 he was briefly the Director of Force Health Protection and then appointed as Director of Mental Health in September 2014.
MGen Downes has deployed on 4 international operations: OP CAVALIER (Bosnia-Herzegovina) in 1994/95; OP MIRADOR (Italy) in 1997 with 416 Squadron in support of operations in Bosnia-Herzegovina; OP PALLADIUM (again in Bosnia-Herzegovina) in 2002/03 as the Task Force Surgeon; and finally OP ATHENA (Afghanistan) in 2008/09 as the Task Force Surgeon, Commanding Officer of the Heath Services Unit, and Commander of the NATO Multinational Role 3 Hospital at Kandahar Airfield.
MGen Downes assumed the role as Surgeon General and Commander of Canadian Forces Health Services Group on 5 July 2017.