An Australian woman who was accused of deliberately serving poisonous mushrooms at a lunch that led to the deaths of three people has been found guilty of murdering them and attempting to murder a fourth person, ending a trial that had gripped the nation.

Erin Patterson, 50, faces a maximum sentence of life imprisonment for the murder charges. The 12 jurors deciding her fate had been sequestered to keep them sheltered from the overwhelming media attention focused on the case.

The charges against Ms. Patterson stemmed from a lunch party nearly two years ago in the rural town of Leongatha, at which she cooked and served beef Wellington.

She had invited her estranged husband, Simon Patterson, who declined to attend. But his parents, Gail and Don Patterson, were there, along with Gail’s sister, Heather Wilkinson, and her husband, Ian Wilkinson.

Three of them died within a week, with symptoms indicative of poisoning by death cap mushrooms. Mr. Wilkinson fell critically ill but survived, and he testified at her trial.

More than 50 witnesses took the stand in the two-month trial. The prosecutor, Nanette Rogers, never specified a motive for the alleged crimes, though she presented evidence of some brewing tension between Ms. Patterson and her husband over child support and other matters.