[1] Greene served as Chief of Staff in the office of Reform Party of Canada leader Preston Manning for four years.
[citation needed] In the two years prior to his Senate appointment Greene was Principal Secretary and Deputy Chief of Staff to Nova Scotia Premier Rodney MacDonald.
[3] In June 2012, the Senate Transport committee on which he was deputy chair issued "The Future of Canadian Air Travel: Toll Booth or Spark Plug?
[4] In December 2012, Greene, along with Senators Mike Duffy from Prince Edward Island and John D. Wallace from New Brunswick, promoted the idea of Maritime Union, a proposal which would require amending the Constitution of Canada.
In a speech to the Halifax West Conservative Riding Association, Greene argued that Maritime Union would reduce the inefficiencies in having multiple provincial governments and bureaucracies for a population one seventh the size of Ontario.
[5] On September 13, 2013, Greene left his position as Vice Chair of the Standing Senate Committee on Transport and became Deputy Government Whip again.
[10] In March 2017, Greene unsuccessfully ran to succeed Claude Carignan as leader of the Senate Conservatives, losing to Larry Smith.