Gu, wife of ousted Communist Party leader Bo Xilai, said "she would accept and calmly face any sentence," the Xinhua news agency reported.
Earlier Friday four senior police officers admitted a coverup of evidence linking her to the killing.
The trial of Gu and family employee Zhang Xiaojun was conducted amid tight security at an intermediate court in Heifei city in China's eastern Anhui province.
Gu's husband, Bo, a fast-rising party official on track to become a Politburo member, was the party chief of the large city of Chongqing before being ousted in March for alleged disciplinary violations.
The trial of Gu, 53, herself a lawyer, is of enormous significance given her husband's stature prior to his downfall and of its timing in advance of China's once-a-decade leadership change set for later this year.
Gu and Zhang are charged in the poisoning death of businessman Neil Heywood in November.
An unnamed source at the trial told the Telegraph a lawyer for Gu, Jiang Min, said blood tests done on Heywood after his death showed non-lethal levels of cyanide. Jiang said the blood tests and the change in body position from when Gu and Zhang left the room to when Heywood's body was found prove a "third individual" was involved.
"Zhang and Gu said they held Heywood down on a bed with his head lying on a pillow and him facing the ceiling. That is how they left him," the source said.
"When police came they found Heywood was lying face down on the bed with his feet hanging off the end. He was turned upside down," the source said the court was told. "The window was open at a 30-degree angle and there was a footprint near the windowsill and footprints outside on the grass."
Earlier, CNN quoted a court official as saying Gu and Zhang Xiaojun had raised no objections to the prosecution's charges.
Xinhua quoted the "prosecuting body" as saying the facts of the two defendants poisoning the victim were clear and that the evidence was substantial enough to hold the two "criminally responsible for intentional homicide."
The court said its verdict will be announced on a date not yet determined.
"After Thursday's session, the court announced an adjournment, and the judgment will be announced on a day yet to be decided," China's official Xinhua News Agency reported. There had not been much prior coverage of the trial or the incident in the Chinese media.
As for the fairness of the trial, Xinhua said the court had given the lawyer access to the defendants and gave the lawyer access to the entire case file.
The report said more than 140 people attended the trial, including relatives and friends of the accused and the victim, diplomats from the British Embassy and representatives from the media.
The report said four police officers suspected of covering up Gu's conduct during the investigation were also charged "with bending the law to achieve personal benefit." The officers were to face an open trial Friday.
Analysts told The New York Times Gu might be spared the death penalty because she allegedly acted out of concern for her son Bo Guagua.