Mijailo Mijailovic said an inner voice told him to attack the popular politician, but the prosecution argues it was premeditated murder, the BBC reported.
"He admits that he attacked Lindh with a knife and that he caused her death but he denies intending to kill her," defense lawyer Peter Althin told the packed Stockholm courtroom as he sought to have the charges reduced from murder to manslaughter.
Chief prosecutor Agneta Blidberg told the court she would prove Mijailovic, 25, had every intention of killing Lindh.
The foreign minister, one of Sweden's most popular politicians, was stabbed as she was shopping in a Stockholm department store Sept. 10. She died the following day.
The trial is being broadcast live on Swedish radio, with millions of people expected to tune in.
2014: The Year in Music [PHOTOS]