The Department of Justice had wanted Anton Geiser deported, saying he hid his service in the Waffen SS from U.S. officials when he immigrated in 1956.
U.S. District Court Judge David S. Cercone on Friday canceled Geiser's certificate of naturalization. He ordered Geiser, 81, to surrender any documents pertaining to citizenship.
"Individuals like Anton Geiser, who assisted the Nazis in their quest to extinguish the lives of millions of innocent men, women and children, do not deserve the benefits of U.S. citizenship," U.S. Attorney Mary Beth Buchanan said in a statement.
Eli M. Rosenbaum, director of the Justice Department's Office of Special Investigations, said the government will work to remove Geiser from the country "as swiftly as possible."
Geiser's attorneys said in a statement they planned to appeal.
"We understand that Judge Cercone has issued an opinion in the case that is adverse to our client. We have not had the opportunity to fully evaluate Judge Cercone's opinion, however we do expect to file an appeal to the 3rd Circuit on behalf of Mr. Geiser," wrote his attorneys, Jay K. Reisinger and Samuel J. Reich.
Geiser, an ethnic German born in what is now Croatia, became an American citizen in 1962. The retired steelworker has lived in Sharon, about 60 miles northwest of Pittsburgh, since June 1960.
Geiser, who does not deny he was a guard at the camps, has said the U.S. visa application did not ask him to reveal his service and that the law did not require him to volunteer information.
He served as an armed SS Death Head guard at the Sachsenhausen camp near Berlin for much of 1943 and then was transferred to an SS officer training camp at Arolsen. There, he escorted prisoners to and from the Buchenwald camp, where tens of thousands of Jews and others were killed. He was at Arolsen until April 1945.
Geiser told federal officials he was drafted into the German military. He denied harming prisoners even though he said he had orders to shoot prisoners who tried to escape, according to court documents.