A federal crackdown on insider trading has nabbed a former executive of the Nasdaq Stock Market.

Donald L. Johnson, 56, pleaded guilty Thursday to one count of securities fraud for trading on confidential information about companies listed on the Nasdaq.

Johnson placed illegal trades from his computer at Nasdaq offices in New York, using an online brokerage account in his wife’s name, the Securities and Exchange Commission said.

From 2006 to 2009, he reaped more than $755,000 in illegal profits, the SEC said.

Amid a wave of insider-trading charges, the case against Johnson places the crime in the stock markets’ inner sanctum.

From his perch at Nasdaq’s “market intelligence desk,” Johnson received advance word of market-moving corporate developments such as changes in company leadership, earnings reports and the fact that a drug for hypertension had won approval from the Food and Drug Administration, the government said.

It was his job to help companies anticipate and analyze how such news would affect trading in their stock, the government said.

But he used the information to place secret trades, sometimes betting stocks would rise and other times betting they would fall, the government said.

For example, the government said, on July 30, 2009, United Therapeutics received an e-mail from the FDA saying its drug Tyvaso had been approved for a form of hypertension. Minutes later, the company’s general counsel forwarded the e-mail to Johnson. Four minutes after receiving that message, Johnson bought 11,500 United Therapeutics shares.

Later that day, the company announced the news and its share price surged. Five minutes after the announcement, Johnson sold his stock at a profit of about $111,000, the SEC said.

Johnson thought he could get away with the insider trading by using his wife’s account, placing relatively small trades just a couple of times a year, said Neil H. MacBride, the U.S. attorney for the Eastern District of Virginia.

In violation of Nasdaq policy, Johnson never disclosed the brokerage account in his wife’s name to the organization, the SEC said.

“This is the insider trading version of the fox guarding the henhouse,” SEC enforcement director Robert Khuzami said in a news release.

Lanny Breuer, head of the Justice Department’s criminal division, called it “a particularly shocking abuse of trust.”

Johnson’s attorney, Jonathan Simms, said Thursday that “today Mr. Johnson chose to accept responsibility for actions done in the past.”

“These charges are in no way indicative of his overall character,” Simms said.

After an earthquake in Haiti, Johnson traveled there to participate in relief efforts, Simms said.

Johnson, who retired from Nasdaq in 2009 and lives in Ashburn, appeared in federal court in Alexandria to enter his plea. He was released on his own recognizance, Simms said.

He could receive a maximum of 20 years in prison and a $5 million fine, MacBride said. But federal sentencing guidelines point to a prison term of 30 to 37 months, the defense attorney said.

Johnson still faces civil charges from the SEC.

His guilty plea comes amid a wave of insider-trading cases involving hedge fund managers, corporate lawyers, management consultants, a former Goldman Sachs board member and an FDA chemist.