Soon after the event began, the Arizona Democrat took the stage to lead the crowd in the pledge of allegiance. After receiving help from her husband, Mark Kelly, to put her right hand above her heart, Giffords enthusiastically recited the pledge, her voice strong and demeanor positive, before leaving the stage to applause.
"It's been a tough year, but we're lucky to have so many people standing w/us," Kelly, a retired Navy captain and astronaut, wrote on his Twitter account.
Prosecutors accuse Jared Lee Loughner, 23, of carrying out the attack, which purportedly targeted Giffords during a constituent meet-and-greet event.
On Saturday, Giffords made her first visit back to the parking lot of the Tucson supermarket where the mass shooting occurred on January 8, 2011, Kelly posted on Twitter and Facebook. Carusone said it was Giffords who "wanted to stop by the Safeway."
"It's a very intense feeling to stand in the space where six people lost their lives ... and her life changed," Carusone, who was there with the congresswoman, told CNN on Sunday. "Some memories started to come back."
They also went to personally thank doctors and nurses at the University of Arizona Medical Center, who cared for her and the other shooting victims after the attack.
Giffords began Sunday by taking a phone call from President Barack Obama to "offer his support."
"The president expressed amazement at the courage and determination Rep. Giffords has shown along her incredible road to recovery, calling her an inspiration to his family and Americans across the country," the White House added in a statement.
Bells rang out around Tucson at 10:11 a.m., the precise moment one year earlier that the shooting occurred, CNN affiliate KMSB reported.
Sunday was capped by the vigil on the University of Arizona campus. Along with Giffords, the participants included Tucson Mayor Jonathan Rothschild, Rabbi Stephanie Aaron and Dr. Peter Rhee, one of Giffords' doctors. The event's emcee was Ron Barber, Giffords' district director who was shot and wounded in last year's incident.
Ross Zimmerman, whose son Gabe was a staffer for Giffords and among those killed, told CNN on Sunday that he hoped the shooting "is not (seen as) the defining feature of the community" and said that good can come out of the violence.
"People can lose their faculties and do terrible things any place in the world," he said. "I would do anything to have Gabe back, but I can't. So what do we do going forward? How do we go forward in ways that help us remember (the victims) and try and do the most positive things we can in response to that?"
Arizona Democratic Party chairman Andrei Cherny released a statement Sunday recalling lessons he said had been learned over "one gut-wrenching, unforgettable year," including that "pure determination combined with love and support can work miracles."
The state's Republican Party issued its own statement, offering its members thoughts and prayers and referring to some post-shooting reactions blaming extreme right-wing thinking and a charged political environment for the attack.
"While our political process was profoundly shaken by this dreadful incident, we have made incredible progress in recovering our hope and faith in (the political) system," the party said.
Sen. Mark Udall, a Colorado Democrat who spoke on his friend Giffords' behalf at a memorial event Sunday, echoed a speech by Obama last winter calling for more political civility and crossing party lines in Washington and beyond. Prior to the shooting, Giffords often voiced a similar sentiment and Udall called her "a bridge builder" who was "crystal clear in her independence" and always willing to work with others to solve problems.
"The goal isn't bipartisanship, it's results," Udall said. "But bipartisanship is the only way to get results. ... In the end, we're not enemies, we are fellow Americans."
Giffords herself is still recovering from her injuries. She has made few public appearances since the incident with some rare exceptions such as casting a vote raising the federal debt ceiling and an interview with ABC's Diane Sawyer.
She has been undergoing intensive rehabilitation in Houston, but has returned to Tucson four times since the shooting, according to her office.
Carusone, the congresswoman's chief of staff, said that Giffords has steadily increased her workload as her condition has improved.
"As the year wore on, we were able to plug the congresswoman in more," she said. "Now we talk regularly over video chats and telephone. She's gotten more and more involved the better she gets."
Giffords still has not definitively settled on whether she will seek re-election this year, with Carusone predicting that decision will come in the coming months.
"I think, for her, it's a personal decision (and) whether she thinks she can do the job up to the standards she holds for herself," Carusone said.
As to Loughner, he potentially faces the death penalty if convicted on charges of murdering six people -- including the chief federal judge of Arizona, John Roll. He has been diagnosed as schizophrenic and has spent time on suicide watch while in custody and is undergoing treatment in Springfield, Missouri.
A federal appeals court in May cleared the way for him to be forcibly medicated over the objections of Loughner and his attorney.