Mr Trent was first elected to Westmount City Council in 1983. From 1983 to 1987, he was the Commissioner of Planning and Redevelopment, responsible for major changes in zoning and heritage legislation. In January 1990, Mr Trent was again elected to Council, becoming the Commissioner of Finance. City spending was frozen since that date - until its forced merger with Montreal on January 1, 2002. 

From 1991 to 2001, Mr Trent was the Mayor of Westmount. He was the moving force behind the 1994-95 restoration and expansion of the Westmount Public Library. From 1991 to 1994, he was a member of the Environment Commission of the Montreal Urban Community (MUC). 

From January 1994 to January 1998, Mr Trent was President of the Conference of Montreal Suburban Mayors. From November 1994 to February 1998, he was Vice-Chairman of the Montreal Urban Community.
 

From 1994 to 2001, Mr Trent was a member of the Executive Committee of the MUC. During 1998, he was a member of the Board of the MUC Transit Commission. From 1999 to 2001, Mr Trent was the Vice-chairman of the Administration and Finance Commission of the MUC.

 

From 1999 to 2001, Mr Trent led the fight against forced municipal mergers on the Island of Montreal - in the courts and in the media. A SOM poll (The Gazette, 2 August 2001) revealed that Mr Trent was the most popular suburban choice for mayor of the new megacity of Montreal, even though he had refused to run. Another SOM poll (La Presse, 25 August 2001) showed that, right across the Island of Montreal, more people had confidence in Mr Trent to run the megacity than in Gérald Tremblay - who was elected mayor two months later.

 

Mr Trent was the instigator of, and a contributor to, the Poitras Report. The release of this report in March 2003 turned municipal demergers into a major provincial election issue, winning twenty seats for the Liberal Party, and leading directly to legislation permitting such demergers. He was the demerger leader across the Island of Montreal. Thirty Quebec cities demerged 1 January 2006, including Westmount.

Mr Trent was re-elected Mayor of Westmount in October 2009, and shortly thereafter was elected President of the Association of Suburban Municipalities of the Island of Montreal. 

Mr Trent wrote a critically-acclaimed history of the 2002 municipal mergers entitled The Merger Delusion, published by McGill-Queen’s University Press in November 2012. His book was a finalist for the Shaughnessy Cohen Prize for the year's best Canadian political book.