Hainse joined the Canadian Forces in 1977 and was commissioned into the Royal 22e Régiment in 1980.

[1] He was deployed during the Oka Crisis in 1990 and again during the North American Ice Storm of 1998.

[1] He became Commanding Officer of 1st Battalion Royal 22e Régiment at Port-au-Prince in Haiti in 1996, Chief of Staff of Land Force Quebec Area in 2001 and Commander of the Bosnia and Herzegovina Task Force in April 2002.

[1] He went on to be senior officer in charge of international operations at the National Defence Headquarters later in 2002, Commander of 5 Canadian Mechanized Brigade Group in September 2004 and Chief of Staff of Canada Command in Ottawa in July 2006.

[2] It was announced on 19 January 2016 that Hainse would be replaced as Commander of the Canadian Army and would serve as the military representative at NATO Headquarters in Brussels.