The 40-year-old Arizona Democrat vows to return to Congress in the memoir, "Gabby: A Story of Courage and Hope," which is set to be released Nov. 15.
The book provides a detailed look at her struggle to relearn how to walk and talk and her painful discovery that 12 others were wounded and six were killed during the Jan. 8 attack.
The congresswoman's husband, former astronaut Mark Kelly, wrote most of the book.
Kelly recalls trying to tell his wife several times what had happened that January morning when Giffords was shot in the head while meeting constituents outside a Tucson grocery store. But she didn't fully understand until March 12.
Kelly writes that after she found out about the six deaths, Giffords was overcome with emotion and had trouble getting through her therapy. That night as they lay in bed, she told Kelly that she felt awful. He held her as she cried.
The book also reveals that Giffords has lost 50 percent of her vision in both eyes as a result of her injuries.
The Associated Press contributed to this report.