Because Mr. Lamont has the party nomination, he will appear first on the ballot.

Mr. Lamont, a successful businessman, wants to attract business by investing in transportation and training workers. The state, he said, can ill afford a massive tax cut as it faces a yawning deficit next year.

“We are at one of those moments where you need someone who is willing to take the slings and arrows of all the lousy choices we have to make,” he said after an event at a union hall here.

“I have a $2 billion deficit as far as the eye can see, and flat or declining revenues,” he added. “I’m running against people who say they’re going to eliminate the income tax. They will tell you what you want to hear. I’ll tell you the truth, but you’re not going to like it.”

Mr. Lamont is likely the most known candidate for governor; he engineered a stunning upset of Senator Joseph I. Lieberman in the 2006 Democratic primary, before losing in the general election to Mr. Lieberman, who ran as an independent. He then ran for governor in 2010, but lost to Mr. Malloy in the primary.

On the Republican side, voters will decide among five candidates, including Mr. Boughton, who also earned the top spot on the ballot by winning the nomination.

His challengers are Tim Herbst, former first selectman in Trumbull and perhaps the most conservative on the group; Steve Obsitnik, of Westport, a Navy veteran and technology entrepreneur; Bob Stefanowski, of Madison, a former chief executive of DFC Global, a payday lending firm; and David Stemerman, of Greenwich, who founded a multibillion-dollar hedge fund.