Palin has spent the last 4-1/2 years battling the newspaper in a lawsuit over an editorial she said falsely linked her to a deadly Arizona mass shooting that left six people dead and then-U.S. congresswoman Gabby Giffords seriously wounded.
The editorial said "the link to political incitement was clear" and that it came after Palin's political action committee circulated a map putting Democrats, including Giffords, under "stylized cross hairs."
The trial marks a rare instance of a major media company defending its editorial practices before an American jury.
Palin bears a high burden of proof in the case, as she must show by clear and convincing evidence that there was "actual malice" involved in the newspaper's editorial writing process.
The U.S. Supreme Court adopted the "actual malice" standard in a landmark 1964 ruling that made it difficult for public figures to win libel lawsuits. Palin has already signaled in court papers that she will challenge that precedent on appeal if she loses at trial.
And two current Supreme Court justices, conservatives Clarence Thomas and Neil Gorsuch, have suggested revisiting that standard.