US Congresswoman Gabrielle Giffords, who survived a gun attack at a public event in Arizona's Tucson last year, said she would resign from Congress and focus on improving her health.
Giffords, in a statement, said that she needs time to focus on her recovery from the injuries and leaving now "is best for Arizona".
The 41-year-old Democrat Congresswoman was among 19 people shot on January 8, 2011 during a meeting in Tucson in which six people had died.
She was elected in 2006 and would have stood for election to a fourth term in November.
"I have more work to do on my recovery, so to do what is best for Arizona, I will step down this week," Giffords, wearing a red suit and speaking slowly, said in a video posted on YouTube that reviewed her career.
"I am getting better every day. My spirit is high. I will return and we will work together for Arizona and this great country. Arizona is my home, always will be. A lot has happened over the past year. We cannot change that. But I know on the issues we fought for we can change things for the better," she said.
"Jobs, border security, veterans We can do so much more by working together. I don't remember much from that horrible day, but I will never forget the trust you placed in me to be your voice. Thank you for your prayers and for giving me time to recover.
"I have more work to do on my recovery so to do what is best for Arizona I will step down this week. I'm getting better. Every day, my spirit is high. I will return and we will work together for Arizona and this great country. Thank you very much," Gifford said in her video speech.
House Speaker John Boehner had praised Gifford's "courage and perseverance" after the weekend tragedy outside a supermarket in Tucson in a statement.
"She will be missed," Boehner, an Ohio Republican, said.
Steny Hoyer of Maryland, the Number 2 Democrat in the House, said he is saddened she decided to step down.
Her action "put her constituents first" by ensuring "her state and district are fully represented," he said.
Earlier this month, Giffords returned to the scene of the shooting outside a supermarket in the city of Tucson.
Jared Loughner, the man accused of the shootings, is being held in a mental health facility.
In May, a federal judge ruled that Loughner, a high school dropout suffering from delusions and hallucinations, was mentally incompetent to stand trial for the shootings.