Last March, when Rob Bresnahan, Jr., a wealthy business executive, was running to represent a competitive House district in northeastern Pennsylvania, he published a letter to the editor in a local newspaper demanding an end to stock trading by members of Congress.

“The trust our political leaders and institutions have from Americans is at a historic low and it’s easy to understand why,” Mr. Bresnahan wrote in the Wilkes-Barre Citizens’ Voice. “Too often we hear about how politicians are making millions of dollars during their time in office, and it is sickening. If we want to restore trust in government and our political leaders, then Congress needs to lead with these policies.”

If elected, Mr. Bresnahan told voters, he would co-sponsor legislation to ban stock trading by members of Congress, a practice he said “needs to come to an end immediately.”

More than two months after being sworn in, Mr. Bresnahan, who defeated a Democratic incumbent last November in one of the most expensive House races in the country, has not introduced or co-sponsored such a bill. Over that time, he has emerged as one of the most active stock traders in the freshman class, according to Capitol Trades, a site that monitors the stock market activity of lawmakers.

Since he took office in January, Mr. Bresnahan has reported 264 stock trades, according to the site. He has purchased up to $1.7 million in stock since taking office, according to his periodic transaction report, and has sold up to $3.03 million.

Lawmakers in both parties have long championed the issue of banning individual stock trading for members of Congress as a way to appeal to growing populist sentiment among constituents. They note that lawmakers have access to classified intelligence reports, meet with chief executives and play a key role in setting economic policies, creating at least the appearance of conflicts.