It may not be the end, though. The woman whose improbable recovery captivated the nation promised, "I will return."
Giffords spent time Monday at her office with other survivors of the shooting rampage that killed six people and injured 13. She hugged and talked with survivors, including Suzi Hileman, who was shot three times while trying to save her young friend and neighbor, 9-year-old Christina-Taylor Green. The little girl died from a gunshot wound to the chest.
"The last time I did this I had Christina's hand," Hileman said. "It was something that was hanging out there, and now it's not."
Others who met with Giffords included Pat Maisch, who was hailed as a hero for wrestling a gun magazine from the shooter that day, and Daniel Hernandez, Giffords' intern at the time who helped save her life by trying to stop her bleeding until an ambulance arrived.
"It was very touching," said Maisch, who was not hurt in the attack. "I thanked her for her service, wished her well, and she just looked beautiful."
Giffords announced Sunday that she would resign from Congress this week to focus on her recovery. Maisch was sad to think that Giffords would no longer be her congresswoman.
"But I want her to do what's best for her," she said. "She's got to take care of herself."
However, an upbeat Giffords hinted that her departure from public life might be temporary. In a message sent on Twitter, she said: "I will return & we will work together for Arizona & this great country."
In her last act in Tucson as a congresswoman, the Democrat visited one of her favorite charities, the Community Food Bank of Southern Arizona.
The food bank established the Gabrielle Giffords Family Assistance Center with $215,000 it received in the wake of the shooting. Giffords' husband and former astronaut Mark Kelly told people who wanted to help Giffords after the shooting that the best way to do so was to donate to one of her favorite charities.
The center has helped 900 families get on food stamps in the last year and offered guidance to needy families seeking assistance with housing, insurance, clothing and other basic needs.
"It's a wonderful thing that she gets to come here and see the center we built," said Bill Carnegie, the food bank's CEO. "But it's also her exit from Congress. I'm concerned about the future."
Giffords' aides had to yell at TV cameramen and reporters who surrounded the congresswoman as she arrived, telling them to back up. Giffords didn't bat an eye and walked with confidence through the crowd and into the building, where she promptly hugged Carnegie and others.
When she saw the center that is named in her honor, she said "Wow" and "Awesome."
When one woman told Giffords, "I love your new hairstyle," she beamed and responded with "Thank you."
Giffords did not address reporters at the center and planned to head to the airport right after her visit. She was expected in Washington on Tuesday for President Barack Obama's State of the Union address.
In her announcement Sunday, Giffords said that by stepping down, she was doing what is best for Arizona.
"I don't remember much from that horrible day, but I will never forget the trust you placed in me to be your voice," she said in a video posted online.
The video showed a close-up of Giffords gazing directly at the camera and speaking in a voice that was both firm and halting.
"I have more work to do on my recovery," the congresswoman said at the end of the two-minute message, appearing to strain to communicate.
C.J. Karamargin, who was Giffords' spokesman until recently, said he can only imagine what she is feeling as she steps down.
"But Gabby would never want to do a job unless she could give everything to it," he said.
"The news of her stepping down was almost more emotional than this time last year because then, she had survived and had a positive prognosis. Now we've got this pause, this comma, in her career ... and she won't be back anytime soon."
Giffords was shot in the head at point-blank range as she was meeting with constituents outside a grocery store. Her recovery progressed to the point that she was able to walk into the House chamber last August to cast a vote.
Giffords' resignation set up a free-for-all in a competitive district.
She could have stayed in office for another year even without seeking re-election, but her decision to resign scrambles the political landscape.
Arizona must hold a special primary and general election to find someone to finish out her remaining months in office. That will probably happen in the spring or early summer. Then voters will elect someone in November for a full two-year term.
Giffords would have been heavily favored to win again.
She was elected to her third term just two months before she was shot, winning by only about 1 percent over a tea party Republican. But she gained immense public support during her recovery.
Among those mentioned as potential candidates were several Republican and Democratic state lawmakers and the name of Giffords' husband, Mark Kelly, although he has publicly quashed such speculation.
A state Democratic party official who met with Giffords on Sunday also suggested that she could return to politics.
Jim Woodbrey, a senior vice chairman of the state party, said Giffords strongly implied at a meeting that she would seek office again someday. He said the decision to resign came after much thought.
"It was Gabby's individual decision, and she was not in any condition to make that decision five months ago," he said. "So I think waiting so that she could make an informed decision on her own was the right thing to do."