The chief executive of Backpage.com, the sex advertising website recently seized by the federal government, pleaded guilty on Thursday to charges in California and Texas, and officials unsealed plea agreements made last week in federal court in Arizona.

The chief executive, Carl Ferrer, pleaded guilty to one charge of conspiracy and three counts of money laundering in California, and to money laundering in Texas, the states’ attorneys general announced. Additionally, the company pleaded guilty to human trafficking in Texas.

The state-level pleas were required by the federal plea agreements Mr. Ferrer and Backpage entered on April 5 in the United States District Court for the District of Arizona. In news releases on Thursday, Attorneys General Xavier Becerra of California and Ken Paxton of Texas described them as major victories in combating human trafficking.

In his federal deal, Mr. Ferrer, 57, pleaded guilty to charges of conspiracy to facilitate prostitution using a facility in interstate or foreign commerce, and conspiracy to engage in money laundering, acknowledging that he had “long been aware that the great majority” of the advertisements on Backpage for “adult” and “escort” services were actually advertisements for prostitution.