From February 2012 until November 2016, Mills was a member of the board of directors of Pacific Rubiales Energy Corp and from April 2013 until the present he has been a director on the board of CGX Energy Inc. Mills is currently the President and CEO of Toronto Partners Inc. and is also founder of Racing Future Inc. where he is currently President and CEO.
When the Liberal Party, under the leadership of Jean Chrétien, formed the government following the 1993 election, he served as Parliamentary Secretary to the Minister of Industry from 1993 to 1996.
These include World Youth Day in 2002 that brought Pope John Paul II to Toronto, and the post-SARS Rolling Stones concert in 2003.
In 1989, Mills organized the Summit on the Environment in Toronto, which attracted approximately 50,000 people and performers such as John Denver and Gordon Lightfoot.
In 2001, with the Assembly of First Nations, Mills organized and co-chaired the Bala Summit on Water (See http://dennismills.com/water-manifesto/), attended by leading experts from Canada and the United States.
In 2004, Mills unveiled his plan for the Toronto Waterfront, which includes a campus of the United Nations University for Peace, as well as an aquarium, plenty of greenspace, affordable housing, and new sporting facilities.
In 2003, he promised in writing to resign in thirty days if an abandoned property known as the Gatekeeper Squat was not turned into community housing.
That said, he did favour civil unions, and stated he would respect any decision derived from a free vote on the issue in the House of Commons.
The reasoning behind this was that Mills believed that "Broadview--Greenwood" was confusing on a federal scale, and because the NDP had registered a web address for Broadview—Greenwood.
After the election, Mills re-joined Magna International where he served as CEO and Vice-Chairman of MI Developments with responsibility for all of the company's global real estate assets including all North American Thoroughbred racetracks.