A day after wife Gabrielle Giffords resigned from Congress, Mark Kelly told ABC News' Bob Woodruff that "it was certainly the right decision," despite the difficulty of stepping down from her position.

"Over the past month or six weeks, she came to realize that she was not going to be in a position to run for re-election," Kelly said today. "The goal had been for her to get back to work and run for re-election but she was aware that wasn't going to happen. She knew that she had to continue with her rehab."

Giffords, an Arizona Democrat, appeared on the House floor Wednesday to deliver her resignation letter, a little more than a year after being shot in the head.

"This past year my colleagues and staff have worked to make sure my constituents were represented in Congress," the Tucson native, 41, wrote in her letter of resignation. "But if I can't return, my district deserves to elect a U.S. representative who can give 100 percent to the job now."

Kelly, a former astronaut, said Giffords planned to remain politically active and that she hoped a moderate like herself would fill her vacant seat.

"She has always been someone who can work across party lines, a very moderate person who brings people together," he said. "She thinks it's very important to have more moderates in Congress. … When she was up there resigning the other day… Did you see who was behind her? It wasn't only Democrats. There was probably an equal number of Republicans."

For now, Giffords is spending five to six days a week in physical, occupational and speech therapy. Kelly said she still struggled with communication but was finding progress with intensive speech therapy.

"She loves being a member of Congress and really cared about the people she represented," Kelly said. "This is the end of a chapter for her but I think the final book hasn't been written."

While Kelly said he was certain his wife will return to public service, he said he will not be running in 2012.

"No way," he said. "I will not be on the ballot. … I'm never one to close any door - there's no point in doing that - but no one needs to worry about me gathering those signatures."