Jon Lord, who was 57, had a heart attack at his home in Calgary on Tuesday night.
Lord was a Progressive Conservative member of the Alberta legislature from 2001 to 2004.
He served two terms as a Calgary alderman between 1995 and 2001, and ran for mayor in 2010 and in 2013.
Lord finished second to incumbent Mayor Naheed Nenshi last October with 21 per cent of the vote.
"I knew Jon well and I was happy to get to know him better during the last two mayoral elections," Nenshi said in a statement.
Nenshi said Lord was the kind of person "you want to debate." He said Lord presented valuable ideas and forced candidates to test their own.
"It was an honour to have him as a challenger because he pushed all of us to be better."
Lord was a community leader, worked for positive change and understood that government is there to serve its citizens, Nenshi said.
"Even if you didn't see eye to eye with him on a particular issue, the debate was always respectful. Our city has lost a champion, and far too soon. He will be greatly missed."
Lord also ran unsuccessfully for the federal Conservative nomination in the Calgary Centre byelection in 2012.
Alberta interim Premier Dave Hancock expressed his condolences on Twitter.
"I'm saddened to hear of my former #ableg colleague's passing. Jon Lord was a great Albertan. Alberta's prayers are with his family," Hancock tweeted.
Danielle Smith, Wildrose Opposition leader in the legislature, tweeted: "He was passionate about public service & will be missed."
Dan Kelly from the Canadian Federation of Independent Business said Lord was a "strong advocate of small business."