"Gabby and I were horrified to hear of the tragedy in Colorado last night. Our thoughts and prayers are with the victims and their families," Mark Kelly said in a posting on Twitter Friday.
Giffords, an Arizona Democrat, suffered brain damage, and six people died in the Jan. 8, 2011, shooting at a grocery store parking lot in Tucson, Ariz.
She resigned from Congress this year to focus on her rehabilitation.
Ron Barber, a Giffords staff member injured in the shooting, won a special election to serve the remainder of her term.
Politico reported Barber said in a statement his "thoughts and prayers" go out to the Aurora community.
"The people of Aurora have suffered an immense loss," the statement said.
"We are tested in times like these and we must come together to support one another in the wake of tragedy. I know that Aurora and its residents will take solace in one another in the coming days and weeks. All of Southern Arizona, and the nation, stands with you today."
The brain damage Giffords suffered affected her speech and language skills.
Police in Colorado said James Eagan Holmes, 24, was being held in the Aurora movie theater shooting in which 12 people were killed and 58 injured. The shooting occurred during a midnight showing of the new Batman movie.