On April 19, 2007, he was selected to be the Official Opposition's Shadow Minister of Environment and Sustaining Development.
He lost his seat in the 2008 election along with 33 other ADQ MNAs, coming in third place in his ridding with 18.46% of the vote.On May 31, 2010, it was announced Diamond had switched to the Liberal Party and would be running for them in the July 5 Vachon by-election.