Barber won a special election to fill Giffords' congressional seat after she stepped down a year after the shooting.
"We are thankful she survived your attempt to take her life," Barber told Loughner. "You did not take away her compassion and desire to serve. In fact, the whole world knows of this great leader. She remains the model of bipartisanship and political courage."
Barber told the court he supports a life sentence for Loughner.
"I hold no hatred for you, but I am very angry and sick at heart about what you have done and the hurt you have caused all of us," Barber told Loughner. "You now must bear this burden and never again see the outside of a prison."
Mark Kelly, who was training for a space shuttle mission when he learned his wife was shot, spoke for her as she watched.
"Gabby would trade her own life to bring back any one of those you savagely murdered on that day," he said. The statement noted each of the dead.
"And then there is what you took from Gabby," Kelly said, looking at Loughner. "Her life has been forever changed. Plans she had for our family and her career have been immeasurably altered. Every day is a continuous struggle to do those things she was once so very good at.
His wife now struggles to walk, an arm is paralyzed and she is partially blind, he said. She stepped down from her position in Congress in January 2012 to focus on her recovery.
"Mr. Loughner, by making death and producing tragedy, you sought to extinguish the beauty of life," Kelly said. "To diminish potential. To strain love. And to cancel ideas. You tried to create for all of us a world as dark and evil as your own. But know this, and remember it always: You failed."
Directing his comments away from Loughner for a moment, Kelly said "There's something else Gabby and I have been spending a lot of time thinking about. "
"The way we conduct politics must change," he said. "Sure, it's easier to win a debate if you can turn your opponent into a demon, but that's not how we move forward. Not only does slash-and-burn politics make Americans cynical about their leaders, but it leads to bad ideas. It creates problems instead of solving the ones we have now.
Kelly concluded with words directed again at the defendant. "Mr. Loughner, pay close attention to this: Though you are mentally ill, you are responsible for the death and hurt you inflicted upon all of us on January 8th of last year," he said. You know this. Gabby and I know this. Everyone in this courtroom knows this. You have decades upon decades to contemplate what you did. But after today. After this moment. Here and now. Gabby and I are done thinking about you."
He pleaded guilty to 19 charges in exchange for the life sentence to avoid facing the death penalty. He had been facing more than 50 federal charges.
"Mr. Loughner, you have been given a gift, whether you know it or not," Assistant U.S. Attorney Wallace Kleindienst said, just before recommending a life sentence. "Almost all the victims you shot and the families of those you killed came to us and said they didn't want us to seek the death penalty in this case."
Under the pleas, Loughner admitted guilt in the wounding of Giffords and the murders of federal employees U.S. District Court Chief Judge John M. Roll, 63, and congressional aide Gabriel M. Zimmerman, 30, prosecutors said.
Loughner also pleaded guilty to the attempted murders of federal employees and congressional aides Ronald S. Barber, 65, and Pamela K. Simon, 63, prosecutors said.
Loughner also admitted causing the deaths of Christina-Taylor Green, 9; Dorothy "Dot" J. Morris, 76; Phyllis C. Schneck, 79; and Dorwan C. Stoddard, 76, prosecutors said.
Prosecutors said Loughner admitted injuring with a Glock pistol 10 people participating at an activity provided by the U.S. government and creating a grave risk of death to 13 more people.
Prosecutors agreed to the plea deal after taking into account Loughner's history of mental illness and the views of victims and their families. The judge in August ruled Loughner competent to stand trial.