WASHINGTON — Joe ­Arpaio, a former Arizona sheriff whose staunch opposition to illegal immigration made him a household name, was convicted Monday of criminal contempt of court for ignoring a judge’s order to stop detaining people he suspected of no crime other than being illegal immigrants.

US District Judge Susan Bolton wrote that Arpaio had shown a flagrant disregard for the court’s command.

‘‘Not only did the defendant abdicate responsibility, he announced to the world and to his subordinates that he was going to continue business as usual no matter who said otherwise,’’ she wrote.

Arpaio faces up to six months in prison at his sentencing, scheduled for October 5. ­Arpaio’s lawyer said he would appeal to get a trial by jury. He had been convicted after a trial in front of Bolton.

‘‘Today, Judge Susan Bolton violated the United States Constitution by issuing her verdict without even reading it to the defendant in public court,’’ Jack Wilenchik, Arpaio’s lawyer, said. ‘‘Her verdict is contrary to what every single witness testified. Joe Arpaio believes a jury would have found in his favor. He is in this for the long haul and will continue his fight to vindicate himself, to prove his innocence, and to protect the public.’’

The legal saga dates back years. In 2011, Arpaio, then sheriff of Maricopa County, was enjoined by US District Judge Murray Snow from detaining people he thought to be illegal immigrants, when they were not charged with any other crimes. Prosecutors alleged that he continued to do so, and last year, the Justice Department decided to pursue a criminal contempt-of-court case against him.

Wilenchik said that the judge’s order enjoining Arpaio was not clear and suggested that Arpaio was merely doing what others do routinely, namely turning over those in the country illegally to the US Border Patrol.

‘‘Numerous law enforcement agencies also continue to do this,’’ Wilenchik said. ‘‘In fact, the DOJ now goes after agencies that refuse to do this.’’

WASHINGTON POST