Standing confidently but at times her voice breaking, she told the same eight men and four women who found her guilty of first-degree murder that she planned to use her time in prison to bring about positive changes, including donating her hair to be made into wigs for cancer victims, helping recycle trash and designing T-shirts that would raise money for victims of domestic abuse.
Arias admitted killing boyfriend Travis Alexander and said it was the "worst thing" she had ever done. But she stuck to her story that the brutal attack - which included stabbing and slashing Alexander nearly 30 times, shooting him in the head and nearly decapitating him - was her defense against abuse.
Her testimony came a day after her attorneys asked to be removed from the case because they felt the five-month trial had become a witch hunt that prompted death threats against a key witness in the penalty phase. They also argued for a mistrial. The judge denied both requests.
Arias acknowledged the pain and suffering she caused Alexander's family, and said she hoped her conviction brought them peace.
"I loved Travis, and I looked up to him," Arias said. "At one point, he was the world to me. This is the worst mistake of my life. It's the worst thing I've ever done."
She said she considered suicide, but didn't kill herself after Alexander's death because of her love for her own family. She displayed a handful of pictures from her childhood, including photos of her family and former boyfriends.
Arias said she regretted that details of her sex life with Alexander came out during the trial, and described a recorded phone sex call played in open court as "that awful tape."
"It's never been my intention to throw mud on Travis' name," she said, adding that she had hoped to reach a deal with prosecutors before the case ever went to trial.
"I was willing to go quietly into the night," Arias said.
The jury paid close attention to Arias as she spoke, their gaze turning to the large screen behind her as she ticked through family photos and explained the stories behind each image. Arias retained her composure throughout much of her statement, pausing occasionally as she apparently cried, but no tears were visible.
Alexander's family sobbed throughout her speech as Arias' mother and father looked on from the other side of the gallery.
After she finished speaking, the judge told jurors they can consider a handful of factors when deciding what sentence to recommend, including the fact that Arias has no previous criminal record. They also can weigh defense assertions that Arias is a good friend and a talented artist.
Judge Sherry Stephens also explained to jurors that their decision would be final, emphasizing the fact that Arias' life is literally in their hands.
"You will determine whether the defendant will be sentenced to life in prison or death," Stephens told the panel. "Your decision is not a recommendation."
The jury will hear closing arguments Tuesday afternoon, then begin deliberating Arias' fate for the June 2008 killing of Alexander in his suburban Phoenix home.
Arias initially claimed she knew nothing about the slaying. Then she blamed masked intruders before eventually arguing self-defense. Prosecutors contend she killed Alexander in a jealous rage because he wanted to end their relationship and go to Mexico with another woman.
Arias' attorneys also tried without success to withdraw from the case after Arias gave her post-conviction TV interview.
"Longevity runs in my family, and I don't want to spend the rest of my natural life in one place," a visibly shaken Arias told Fox affiliate KSAZ from a holding cell inside the courthouse. "I believe death is the ultimate freedom, and I'd rather have my freedom as soon as I can get it."
Last week, Alexander's brother and sister tearfully described for the jury how Alexander's death has torn apart their lives. Defense attorneys had planned to call witnesses, including a female friend and ex-boyfriend of Arias, to speak on her behalf. But after the judge denied all their motions on Monday, they said Arias would be the only one speaking to jurors.
Defense attorneys claimed the female friend had received death threats and refused to testify. They then argued Arias could not receive a fair trial in the penalty phase without the witness, but the judge disagreed.
Instead, Stephens simply told jurors the woman was supposed to testify about Arias' "abusive environment she grew up in and abuse as an adult," but was now unavailable to appear in court.
Arias told jurors the friend and her young son had been "threatened and harassed."