Armin Meiwes, 42, went on trial on Wednesday. Television images showed him, dressed smartly in jacket and tie, laughing and chatting to his lawyer in Kassel, central Germany.
It is the first time he has been shown in public since his arrest.
The computer technician said in the past few days that he regretted what had happened, but was only doing what was asked of him.
In an interview on Tuesday, Meiwes said it was not a case of murder because the victim "used me as a tool" to help him die.
"My friend enjoyed dying, death. I only waited horrified for the end after doing the deed. It took so terribly long," he said.
Murder, say prosecutors
Prosecutors, however, have accused him of murder for sexual satisfaction, arguing that though his victim had an apparent death wish, Meiwes was already intent on killing him.
Defence lawyers argue that, at worst, he is guilty of "killing on demand," which would be punishable by up to five years in prison.
"My friend enjoyed dying, death. I only waited horrified for the end after doing the deed. It took so terribly long"
If found guilty of murder, Meiwes would be liable to life in prison. He is also accused of "disturbing the peace of the dead" for carving up the body.
Meiwes has said he made contact with his victim, Bernd Juergen Brandes, on the internet after advertising for someone willing to be killed and eaten.
Brandes travelled to his house in Rotenburg, near Kassel.
Meiwes later stabbed him, carved up the body, ate some of the flesh, stored the rest in a deep-freezer and buried the bones and the skull in his garden.
The whole act was recorded on video, again with the apparent agreement of Brandes.
It is unclear if the videos taken during the incident in March 2001 would be shown publicly in court or behind closed doors. Investigators who have scanned them have spoken of scenes like "in a horror film."
The case has no legal precedent in Germany, where cannibalism is not listed as a crime, and has gripped the country since Meiwes's arrest last year.
The case came to light after a student spotted another advertisement placed by Meiwes on the internet and alerted police.
Officers studied the 16 computers, 221 hard drives, 95 CD-Roms, nearly 1800 diskettes and 307 videos found at his home to tap into a hitherto hidden cannibal scene.