Lantz defeated James Aylward and Darlene Compton in a leadership race on that saw nearly three-thousand votes cast.
Lantz is not a member of the legislature, but spent eight years as a city councillor in Charlottetown.
He replaces interim leader Steven Myers.
The Progressive Conservatives currently hold three of the 27 seats in the legislature.
Lantz says his first task will be to prepare his party for the next election.
"Our opponents think we aren't ready, and that now is the time to strike and claim another four years of government for themselves. They are wrong," he said.
"Starting Monday we'll mobilize, district by district, poll by poll. We already have candidates in place."
The governing Liberals held their own leadership convention last weekend. Wade MacLauchlan was unopposed for the position, replacing Robert Ghiz as leader and premier.
The next provincial election could be held as late as April 2016, but in his acceptance speech Lantz said he believes the government is already preparing to call a vote sooner.
Lantz said he is aware of the challenges ahead of him.
"I'm a realist. This province has serious problems. We've been left with a debt that our children and grandchildren will spend the rest of their lives paying for," he said.
Saturday's leadership convention saw a record-setting number of votes cast, said John Maynard, the party's chief returning officer.
The convention used a preferential ballot system that meant each member voted only once, either in advance or on Saturday.
Lantz comes into the position having worked for 16 years with health technology company DeltaWare Systems, according to his campaign website.Suggest a correction