The secret ballot vote held this morning saw Duplessis earn 15 of the votes, compared to only three for the other candidate, Jacques St-Jean.
"I accept this position, and feel we must implement every possible means to demonstrate to our fellow-citizens that they have rightly placed their trust in us," Duplessis said on Friday.
Laval's long-serving former mayor, Gilles Vaillancourt, stepped down on Nov. 9 amid mounting corruption allegations.
Vaillancourt led Laval, Quebec's third largest city, for 23 years.
Earlier this week, the 20 councillors who were a part of Vaillancourt's PRO des Lavallois party announced they would sit as independents.
In a statement released following Duplessis' election, the city said it would turn over the almost $950,000 it received following the dissolution of the party to the Quebec director-general of elections for verification before the new municipal government will use the money.
In that same statement, Duplessis said the city is now entering into an era of greater transparency, teamwork and dialogue.
The new mayor will serve until the municipal election next fall.
New Laval mayor looked up to Gilles Vaillancourt
Duplessis has been councillor of Laval's St. Martin district since 2005. He joined the executive committee in 2009.
The 42-year-old chartered accountant refers to Vaillancourt as his mentor. He is the father of two girls and was born in Laval.
Emilio Migliozzi is a member of the Mouvement Lavallois party, which has no seats on city council. He is concerned that nothing will change at city hall, because Duplessis and the other members of council were former members of the Vaillancourt's party.
"This is a perfect clone of Mayor Vaillancourt's administration. Nothing has changed. You can change the ingredients but it's always the same people … who are going to make the decisions," he said.