U.S. District Judge Dale Kimball wrote in a 149-page ruling that Brian David Mitchell, 56, "does not presently suffer from a mental disease or defect that impedes his rational and factual understanding" of the proceedings against him.
A court hearing is scheduled on March 26 to set a trial date.
The ruling follows a 10-day competency hearing held for Mitchell last year, where experts who testified split in their opinions about Mitchell's competency.
The prosecution's expert, New York forensic psychiatrist Dr. Michael Welner, concluded the Mitchell suffers from a range of disorders, including pedophilia, anti-social and narcissistic personality disorders, but said he was not psychotic or delusional.
The key expert for the defense, Dr. Jennifer Skeem, diagnosed Mitchell with a delusional disorder and said he was incompetent.
But the judge agreed with Welner, who said Mitchell was faking mental illness to avoid responsibility for wrongdoing. Welner described Mitchell as an "effectively misleading psychopath" who has duped those around him into thinking he is incompetent.
During many court proceedings Mitchell has been removed from court because he breaks into song, disrupting proceedings.
"The court agrees with Dr. Welner that Mitchell's singing in court is a contrivance to derail the proceedings and create the false impression that he is unable to control his behavior," Kimball wrote.
Mitchell's court-appointed attorney, Robert Steele, did not immediately return a call from The Associated Press on Monday.
Carlie Christensen, the acting U.S. Attorney for Utah, applauded the ruling Monday, calling it a significant step in holding Mitchell accountable.
"Elizabeth Smart, her family and this community have waited many years for resolution of this case," Christensen said.
Mitchell was indicted in federal court in 2008 on charges of kidnapping and unlawful transportation of a minor across state lines.
Smart was 14 when she was kidnapped from her home in 2002. She was found nine months later, in March 2003, walking a suburban Salt Lake City street with Mitchell and his now-estranged wife, Wanda Barzee.
Smart, now 22, testified for the competency hearing in October, saying she was raped after a marriage ceremony staged by Mitchell.
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Associated Press Writer Jennifer Dobner contributed to this report.
