The former congresswoman's jump will be broadcast on NBC's "Today" show on Thursday.
Giffords still struggles to speak and walk, but has become a leader of Americans for Responsible Solutions, a national organization she founded with her husband, Mark Kelly, to rival the powerful pro-gun lobby.
The group struggled to bring about any major change at the federal and state level in its first year of existence, but the couple is confident they laid the groundwork for success in future election cycles.
"The legacy of any day where there's a mass shooting and loss of life is, I think, a chance to reflect on who these people were and what they did, particularly the people who died," Kelly, a former astronaut, said in an interview with The Associated Press on the eve of the anniversary. "But it's also a chance to look forward and see how we can make changes and reduce the numbers of instances like this that we have."
Officials this week announced plans for a permanent memorial in remembrance of the shootings expected to be located downtown at the Old Pima County Courthouse and in an adjacent park. The sites would display some of the thousands of items, including letters, candles and American flags that were placed in storage after forming makeshift memorials across the city in the days after the shooting.
Some of the items will be on display Wednesday at libraries in Tucson.
"Like any community that experiences a tragedy, the citizens want to be connected to it in some way to show their appreciation and understanding and sympathy," said Stephen Brigham, president of the January 8 Memorial Foundation. "Everyone we talked to reinforced the importance of providing a place to go and remember that tragedy, but also a place to remember and celebrate how the community responded."
Giffords and Kelly formed their organization just weeks after the massacre in Newtown, Conn.
Since then, a divided Congress has done nothing to tighten any of the nation's gun laws. Some states, including Colorado and Delaware, pushed ahead with their own gun-control measures, while others, like Arizona, Giffords' home state, moved in the opposite direction, passing a law that requires municipalities to sell weapons surrendered at buyback programs aimed at getting more guns off the streets instead of destroying them.
Kelly said his group has signed up more than a half-million people, and between January 2013 and July 2013, they raised more than $11 million. He pointed to the successes in Colorado and Delaware in enhancing background checks.
"So we're going to have the resources to be effective in the next election cycle in 2014," he said.
Kelly is a gun owner and supporter of the Second Amendment who wishes he could work with organizations like the National Rifle Association to preserve gun rights while also keeping weapons out of the hands of dangerous criminals and the mentally unstable.
He worries that if mass killings continue and responsible laws aren't passed, "you get to a point where other people start to question the Second Amendment."
In an opinion piece for The New York Times on Wednesday, Giffords writes about her struggles to recover, calling it "gritty, painful, frustrating work, every day."
"I had planned to spend my 40s continuing my public service and starting a family. I thought that by fighting for the people I cared about and loving those close to me, I could leave the world a better place. And that would be enough," she wrote. "Instead, I've spent the past three years learning how to talk again, how to walk again."
Still, Giffords says she will not give up.
"We're not daunted. We know that the gun lobby, which makes money by preventing sensible change, relies on dramatic disappointments to wound us, reduce our power, push us back on our heels," Giffords wrote. "Our fight is a lot more like my rehab. Every day, we must wake up resolved and determined."
Jared Lee Loughner was sentenced in November 2012 to seven consecutive life sentences, plus 140 years, after he pleaded guilty to 19 federal charges in the shooting.
Giffords, an Arizona Democrat, resigned from Congress as she continues to recover from her injuries.
Tucson Mayor Jonathan Rothschild will participate in a bell-ringing ceremony Wednesday morning, one of several events planned in the city.
"The wounds are still there. Time helps, but it doesn't heal all the wounds," Rothschild said. "I think the commemorations are, in large part, recognition of our community's collective care and compassion and grit to go on."
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