A Turkish-Iranian gold trader whose prosecution in Manhattan drew sharp criticism from Turkey’s president has pleaded guilty and is cooperating with the American authorities, a federal prosecutor disclosed in court on Tuesday.

The trader, Reza Zarrab, who is being held by the authorities at an undisclosed location, pleaded guilty on Oct. 26 to all seven counts against him, including conspiracy to violate the United States sanctions against Iran, newly unsealed court records show.

Mr. Zarrab is expected to testify on Wednesday as a government witness in the trial of a Turkish banker, Mehmet Hakan Atilla, that began this week in Federal District Court. Mr. Zarrab, Mr. Atilla, and seven other defendants were charged with participating in a billion-dollar scheme to smuggle gold for oil in violation of the Iran sanctions.

On Tuesday, in his opening statement to the jury, the prosecutor said the men had used front companies and false documentation, told lies to American officials and paid bribes at the highest levels of the Turkish government.